The iShares Nasdaq Biotechnology ETF (NASDAQGM: IBB), the largest biotech ETF by assets, and its equal-weight rival, the SPDR S&P Biotech ETF (NYSEArca: XBI) tumbled on Tuesday, extending losses that have put those bellwether biotech funds in correction territory.

With Tuesday’s decline, IBB is down 10% over the past month while XBI is lower by more than 9%. A decline of 10% from a recent high is the standard definition of a correction. IBB, which holds nearly 190 stocks and is a cap-weighted ETF, has a price-to-earnings ratio of just over 21 and a price-to-book ratio of 4.92. The ETF’s three-year standard deviation is just over 25 percent.

Some market observers believe the recent declines among biotechnology stocks could signal a buying opportunity for prescient investors.

“This move comes on the back of a string of disappointing earnings for mega-cap biotech in late October, said Chad Morganlander, portfolio manager at Washington Crossing Advisors; he pointed specifically to disappointments from Gilead and Celgene. Still, he likes the space,” reports CNBC.

Healthcare stocks are also showing attractive valuations relative to other defensive sectors, which are richly valued. Biotechnology historically trades at multiples that are elevated relative to broader benchmarks, but after last year’s of struggles for biotechnology names, some analysts see value with some big-name biotech stocks.

Related: Hot Biotech Stocks, ETFs Can Keep Surging

Biotech “trades more than 25% below its 15-year average based on historical and forward price-to-earnings ratios. Compared with the broader market, biotech stocks are also trading at a discount and far below their historical average,” according to State Street.

“One of the things that people are worried about is, are we going to get a repeat of what we saw in 2015, when the IBB crashed 40 percent in just six months. But the set-up is much, much different than it was back then,” said Matt Maley, equity strategist at Miller Tabak, according to CNBC.

ETF traders who are betting big on the biotechnology sector rebound have also utilized leveraged long options including the Direxion Daily S&P Biotech Bull Shares (NYSEArca: LABU), which takes the 3x or 300% daily performance of the S&P Biotechnology Select Industry Index.

For more information on the biotech sector, visit our biotechnology category.