The short interest data are out for the September 30 settlement date. Biotech companies are considered a riskier group of stocks, with big upside and big downside. FDA rulings can make or break them. A single failed clinical trial can mean disaster for a stock. 24/7 Wall St. has reviewed the top biotech companies, without focusing on speculative companies.

The September 30 short interest data have been compared with the previous figures, and short interest increased in most of these selected stocks for this settlement date.

Amgen Inc. (NASDAQ: AMGN) saw its short interest jump to 11.01 million shares from the previous level of 10.4 million. Shares closed Friday at $149.59, in a 52-week trading range of $127.67 to $181.81.

Biogen Inc. (NASDAQ: BIIB) had its short interest rise to 5.15 million shares from the previous 4.59 million. Shares closed Friday at $269.16, within a 52-week trading range of $265.00 to $480.18.

Celgene Corp. (NASDAQ: CELG) short interest for this settlement date increased to 16.53 million shares from the previous reading of 14.95 million. Shares of Celgene closed Friday at $117.38, in a 52-week range of $83.16 to $140.72.

Gilead Sciences Inc. (NASDAQ: GILD) saw its short interest drop to 28.39 million shares, from 29.60 million in the previous period. Shares closed Friday at $100.65, in a 52-week trading range of $85.95 to $123.37.

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MannKind Corp. (NASDAQ: MNKD) saw its short interest increase very slightly to 126.84 million shares. The previous reading was 126.66 million. This is the highest reading on the year. Shares closed Friday at $3.05, in a 52-week trading range of $2.98 to $7.88.

Alexion Pharmaceuticals Inc. (NASDAQ: ALXN) short interest decreased to 6.62 million from the previous level of 6.66 million. The mid-June level was far and away the highest reading on the year, and since that time shares have backed off significantly. Shares closed Friday at $161.08, in a 52-week range of $142.02 to $208.88.

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