With a couple of exceptions, the short interest in biotech stocks is on the rise again, judging by the short interest changes from September 14 settlement date versus the August 31 settlement date. Short interest had largely waned in the previous period.

We have tracked the key short interest changes in the following biotech and emerging pharma companies: Alexion Pharmaceuticals Inc. (NASDAQ: ALXN), Amgen Inc. (NASDAQ: AMGN), Arena Pharmaceuticals Inc. (NASDAQ: ARNA), Biogen Idec Inc. (NASDAQ: BIIB), Celgene Corp. (NASDAQ: CELG), Dendreon Corp. (NASDAQ: DNDN), Gilead Sciences Inc. (NASDAQ: GILD), Illumina Inc. (NASDAQ: ILMN), Onyx Pharmaceuticals Inc. (NASDAQ: ONXX), Pharmacyclics Inc. (NASDAQ: PCYC), Regeneron Pharmaceuticals Inc. (NASDAQ: REGN), Vertex Pharmaceuticals Inc. (NASDAQ: VRTX) and VIVUS Inc. (NASDAQ: VVUS). We also tracked the iShares Nasdaq Biotechnology (NASDAQ: IBB) against the group.

Alexion Pharmaceuticals Inc. (NASDAQ: ALXN) short interest rose 2.0% between August 31 and September 14 to 5.38 million shares. Days to cover has risen to almost six.

Amgen Inc. (NASDAQ: AMGN) saw short interest decline 2.2% to 12.61 million shares. Days to cover slipped to less than three.

Arena Pharmaceuticals Inc. (NASDAQ: ARNA) short interest rose 4.0% to 45.67 million shares. The average daily volume was the lowest it has been since April. But short interest was 21.2% of the float.

Biogen Idec Inc. (NASDAQ: BIIB) shares sold short grew 4.8% to 2.22 million. Short interest was 1.0% of the float.

Short interest in Celgene Corp. (NASDAQ: CELG) rose 3.1% to 6.05 million shares.

Dendreon Corp. (NASDAQ: DNDN) short interest increased 1.8% to 43.08 million shares. This was 28.6% of the float.

Gilead Sciences Inc. (NASDAQ: GILD) short interest was up 9.3% to 20.61 million shares. Days to cover slipped to about three.

Illumina Inc. (NASDAQ: ILMN) saw short interest rise 8.8% to 25.77 million shares. That was the fifth consecutive period of increasing short interest. Short interest was 21.3% of the float.

Onyx Pharmaceuticals Inc. (NASDAQ: ONXX) shares sold short increased 2.6% to 5.49 million. Days to cover jumped above five. Short interest was 8.6% of the float.

Pharmacyclics Inc. (NASDAQ: PCYC) short interest retreated 5.7% to 4.91 million shares. Days to cover fell to less than five. Short interest was 9.0% of the float.

Regeneron Pharmaceuticals Inc. (NASDAQ: REGN) short interest rose 8.4% to 5.19 million shares. Short interest was 6.9% of the float.

Short interest in Vertex Pharmaceuticals Inc. (NASDAQ: VRTX) grew 2.8% to 6.47 million shares. Days to cover is about five.

VIVUS Inc. (NASDAQ: VVUS) short interest was up 2.1% to 16.07 million shares. Days to cover jumped to about 10. Short interest was 16.1% of the float.

To show how the sector has held up: the iShares Nasdaq Biotechnology (NASDAQ: IBB) ETF closed at $141.76 on the same date. Its current 52-week range is $87.67 to $145.23.

Trey Thoelcke

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