In frustrating news for some short sellers, the iShares Nasdaq Biotechnology ETF (NasdaqGM: IBB) is up 7.5% in the past month and nearly 15% from its April trough.

Now the largest biotech ETF by assets is facing its first legitimate tussle with a key resistance level following its bounce from its April low.

“Did Bio-Tech hit a long-term high on the week of February the 28th? The jury is still out on this question I feel. We could find out a good deal about this question in the next week,” said Chris Kimble of Kimble Charting Solutions. “Bio-Tech peaked around the first of March and fell for six weeks (declining around 20%)  then it reversed the decline, moving higher since April the 15th. The rally has recovered 61% of the decline and now has IBB kissing the underside of a key support line.”

Although biotech stocks and ETFs have surged for almost two months, the rally remains unloved. More than 8.2 million shares of IBB are sold short, an amount that would take almost six trading days to cover, according to Nasdaq data.

The SPDR S&P Biotech ETF (NYSEArca: XBI), the second-largest biotech ETF, is up almost 10% this week, but it is also one of the most heavily shorted U.S. ETFs.

Since the start of the second quarter, of the five major biotech ETFs, only the First Trust NYSE Arca Biotechnology Index Fund (NYSEArca: FBT) has seen inflows while the other four biotech ETFs have seen combined outflows of over $400 million. [A Hated Biotech Rally]