Avantor (AVTR) Slid on Lower Than Expected Guidance

Soumya Eswaran Mon, May 18, 2026 at 9:09 AM EDT 3 min read **

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Longleaf Partners, managed by Southeastern Asset Management, released its first-quarter 2026 investor letter. A copy of the letter is available to download here. The Fund returned -4.46% in the quarter, compared to the S&P 500’s -4.33% and the Russell 1000 Value Index’s 2.10% return. The year began similarly to the second half of 2025, with rising stocks and penalization for caution. February was marked by unusual sector-wide movements influenced by perceived AI outcomes. Complications arose from the Iran War and increasing private credit risks. The Fund initially lagged the market, but performance improved as conditions worsened. The fund ended the quarter with a P/V of mid-50s%, which bodes well for promising future returns. In addition, please check the Fund’s top five holdings to know its best picks in 2026.

In its first-quarter 2026 investor letter, Longleaf Partners Fund highlighted Avantor, Inc. (NYSE:AVTR). Headquartered in Radnor, Pennsylvania, Avantor, Inc. (NYSE:AVTR) provides mission-critical products and services to biotechnology, education, and pharmaceutical companies. On May 15, 2026, Avantor, Inc. (NYSE:AVTR) closed at $7.62 per share. One-month return of Avantor, Inc. (NYSE:AVTR) was -10.35%, and its shares lost 42.96% over the past 52 weeks. Avantor, Inc. (NYSE:AVTR) has a market capitalization of $5.20 billion.

Longleaf Partners Fund stated the following regarding Avantor, Inc. (NYSE:AVTR) in its Q1 2026 investor letter:

"Avantor, Inc.** (NYSE:AVTR) – Life-sciences company Avantor detracted for the quarter. The stock price declined due to new CEO Emmanuel Ligner providing a 2026 outlook lower than expectations, with bioprocessing revenues expected to be stagnant vs. other peers guiding for growth in 2026. We believe self-inflicted but fixable production inefficiencies are the cause, and the appointment of Mary Blenn as COO is a positive given her supply chain and operational experience at Cytiva and GE Healthcare. We believe this new team is correcting previous missteps that will enable improved revenue growth and margin improvement. Avantor continues to produce solid FCF, and several directors recently demonstrated confidence with substantial open market purchases."

Is Avantor, Inc. (AVTR) The Most Undervalued Stock With Smart Money Ratings? Avantor, Inc. (NYSE:AVTR) is not on our list of 40 Most Popular Stocks Among Hedge Funds Heading Into 2026. According to our database, 40 hedge fund portfolios held Avantor, Inc. (NYSE:AVTR) at the end of the fourth quarter, compared to 50 in the previous quarter. In Q1 2026, Avantor, Inc. (NYSE:AVTR) reported $1.58 billion of revenue, which was down 4% on an organic basis and flat year-over-year on a reported basis. While we acknowledge the potential of Avantor, Inc. (NYSE:AVTR) as an investment, we believe certain AI stocks offer greater upside potential and carry less downside risk. If you're looking for an extremely undervalued AI stock that also stands to benefit significantly from Trump-era tariffs and the onshoring trend, see our free report on the best short-term AI stock.

Story Continues In another article, we covered Avantor, Inc. (NYSE:AVTR) and shared the list of best medical stocks to buy under $30. In addition, please check out our hedge fund investor letters Q1 2026 page for more investor letters from hedge funds and other leading investors.