RGEN vs TMO: Which Is the Better Buy in 2026?

Same yardstick, side by side (as of September 2026). Valuation lined up like this is most meaningful for two names in the same corner of the market, which these are. Figures are approximate; verify before investing.

Reading it: TMO is the cheaper of the two on forward earnings, but cheaper is not the same as better. Pair the valuation with growth (how far the forward P/E sits below the trailing P/E) and risk (beta) before you decide.

The metrics above tell you which is the marginally better business. The bigger risk for most people is not picking the slightly worse stock, it is over-concentrating. RGEN and TMO share themes, so owning both, or adding either to what you already hold, can quietly push a large share of your portfolio into one bet.

This is the part a generic comparison page cannot answer, because it depends on what you own. Connect your brokerage and Walnut shows your real, combined RGEN and TMO exposure, flags overlap with your existing positions, and tells you if adding one would tip you past a concentration you are comfortable with, read-only by default, with your login staying at your broker. Walnut is not an investment adviser.

Repligen Corporation makes consumable products and equipment used to manufacture biologic drugs, including monoclonal antibodies, gene therapies and vaccines. Its portfolio spans four franchises: filtration (KrosFlo and XCell ATF systems), chromatography resins and columns, proteins (notably Protein A ligands used to purify antibodies), and process analytics. Because roughly 80% of its offerings face limited direct competition and its consumables are embedded in customers' validated manufacturing processes, Repligen sells into a durable, recurring bioprocessing demand base rather than one-off equipment cycles.

Full RGEN guide

Thermo Fisher Scientific, headquartered in Waltham, Massachusetts, is a global provider of scientific instruments, consumables, reagents, and services used across pharmaceutical and biotech drug development, clinical diagnostics, academic research, and environmental and industrial testing. The company operates through four reportable segments: Life Sciences Solutions (reagents, proteins, and consumables for research and bioproduction), Analytical Instruments (mass spectrometers, chromatography systems, electron microscopes, and laboratory equipment), Specialty Diagnostics (clinical diagnostic kits and transplant diagnostics), and Laboratory Products and Biopharma Services (supply-chain distribution, contract research through PPD, and contract drug manufacturing through Patheon). Revenue is generated through instrument sales, high-margin consumables and reagents that customers repurchase continuously, long-term service contracts, and growing contract development and manufacturing (CDMO) fees; consumables and services collectively account for a majority of annual sales and provide durable recurring revenue.

Full TMO guide

Both fit overlapping themes, but they are not interchangeable. The useful comparison is which set of drivers and risks you want exposure to.

• RGEN drivers: Bioprocessing recovery and organic reacceleration; New modalities and consumables mix.
• TMO drivers: Bioprocessing and Biologic Drug Manufacturing Tailwind; Recurring Consumables and Reagents Engine.

A faster-growing, richer-valued name usually swings harder, so it suits a longer horizon and a higher tolerance for volatility; a steadier, more cash-generative business suits a more conservative or income-minded investor. The honest test is which set of risks you could hold through a drawdown: Repligen trades at a rich valuation (around 8 times sales), so any stumble in organic growth or guidance can trigger sharp multiple compression. For TMO, the most significant near-term risk is a contraction in research funding from government agencies (including NIH) and from biotech companies whose access to capital markets has historically been cyclical; when funding tightens, customers delay instrument purchases and reduce consumable orders, pressuring organic revenue growth.

Growth-minded investors who believe the theme has years to run tend to accept the richer multiple for more upside; value-minded investors lean toward the cheaper forward earnings and steadier profile. Pick RGEN if you believe its drivers more; TMO if you believe its. Many investors hold both, but since they share themes, that is a concentrated bet, not diversification. Decide deliberately and check overlap. For the full detail, see the RGEN and TMO guides.

RGEN. Repligen carries a premium valuation typical of high-quality life-science tools names, with a price-to-sales ratio near 8 despite mid-teens headline revenue growth. Management raised its 2026 profit outlook while roughly holding revenue guidance, reflecting a recovery that is more visible in margins than in top-line acceleration so far. The shares are widely viewed as fully priced on sales even if cash flow looks more reasonable.

TMO. Thermo Fisher's trailing price-to-earnings ratio of roughly 26x sits approximately 18% below its own ten-year historical average of about 32x, reflecting a period of softer organic growth as the post-pandemic diagnostics and COVID-related revenue tailwind has faded. The adjusted operating margin of 22.7% for 2025 and management guidance for 6 to 8 percent adjusted EPS growth in 2026 suggest the earnings recovery is progressing, though the pace of organic revenue acceleration remains a key variable the market is watching. Free cash flow of roughly $6.3 billion gives the company significant flexibility for continued share repurchases, dividends, and acquisitions.

Headline figures (approximate, JULY 2026): RGEN shows revenue (ttm) ~$708M, fy2026 revenue guidance ~$810M to $840M, q1 2026 revenue growth ~15% reported (11% organic), fy2026 adjusted eps guidance ~$1.97 to $2.05; TMO shows revenue (full year 2025) ~$44.6 billion, revenue guidance (full year 2026) ~$46.3 to $47.2 billion, adjusted operating income (full year 2025) ~$10.1 billion, adjusted operating margin (full year 2025) ~22.7%.

RGEN and TMO are related but distinct: same themes, different businesses and risks. Neither wins in the abstract; the right pick is whichever thesis you actually believe, sized so you are not over-concentrated in one theme. Walnut can show your combined RGEN and TMO exposure against your real portfolio. It is not an investment adviser.