Biotech stocks are in the red, with the iShares Biotechnology Index (IBB) down by 2.6% early in the U.S. trading session.
Alexion Pharmaceuticals and Gilead Sciences are the biggest losers in the S&P 500, down 4.2% and 3.7% respectively.
This follows Friday’s 4.7% sell-off in the IBB.
All of this comes as market-watchers continue to debate whether or not the sector is in a bubble.
“I don’t think it is a bubble,” said Rich Bernstein in an email to Business Insider. “It’s certainly very speculative, but speculation alone doesn’t make a bubble.”
Reformed Broker Josh Brown, however, point blank believes this is a bubble.
“Anyone with a protein compound under a microscope and a clean suit can go public right now,” said Brown.
According to Renaissance Capital, 37 U.S. biotech firms went public in 2013 and already 24 have gone public through March 20 of this year.
Other big losers in the market include past high-flyers like Netflix (-3.3%), Facebook (1.7%), and First Solar (-1.1%).