The short interest in biotech stocks is generally falling, judging by the short interest changes from August 31 settlement date versus the August 15 settlement date. 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 fell just 0.2% between August 15 and August 31 to 5.27 million shares, the smallest number of shares sold short since the mid May reading.

Amgen Inc. (NASDAQ: AMGN) short interest rose 8.8% to 12.89 million shares. The average daily volume was the lowest it has been this year.

Arena Pharmaceuticals Inc. (NASDAQ: ARNA) short interest rose 2.7% to 43.93 million shares. Days to cover has increased to nearly four.

Biogen Idec Inc. (NASDAQ: BIIB) short interest fell 5.6% to 2.12 million shares. The average daily volume was the lowest it has been this year. Short interest was 0.9% of the float.

Celgene Corp. (NASDAQ: CELG) short interest declined 8.4% to 5.86 million shares. That was its lowest level this year.

Dendreon Corp. (NASDAQ: DNDN) short interest fell 2.4% to 42.31 million shares. This decline ended a five-period streak of rising short interest. Days to cover is up to 12 and short interest was 28.1% of the float.

Gilead Sciences Inc. (NASDAQ: GILD) short interest dropped 10.4% to 18.85 million shares. That followed a 16.6% percent rise in the previous period. Average daily volume fell 33.2% between August 15 and August 31.

Illumina Inc. (NASDAQ: ILMN) short interest rose 7.2% to 23.68 million shares. Days to cover slipped to less than 24.

Onyx Pharmaceuticals Inc. (NASDAQ: ONXX) short interest fell 6.7% to 5.35 million shares. That was its lowest level since March. Short interest was 8.4% of the float.

Pharmacyclics Inc. (NASDAQ: PCYC) short interest retreated 2.3% to 5.21 million shares. Average daily volume was the lowest it has been since mid May. Short interest was 9.6% of the float.

Regeneron Pharmaceuticals Inc. (NASDAQ: REGN) short interest fell 3.7% to 4.79 million shares. Short interest was 6.4% of the float.

Vertex Pharmaceuticals Inc. (NASDAQ: VRTX) short interest declined 1.6% to 6.29 million shares. Days to cover is more than four.

VIVUS Inc. (NASDAQ: VVUS) short interest fell 4.2% to 15.73 million shares. Days to cover rose to more than six. Short interest was 15% of the float.

To show how the sector has held up: the iShares Nasdaq Biotechnology (NASDAQ: IBB) ETF closed at $136.38 on the same date. Its current 52-week range is $87.67 to $141.52.

Trey Thoelcke

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