Bioscience shares held fast Friday to gains made in five priorsessions. The AMEX Biotechnology Index gained 13.93 points,or 9.7 percent, in the week to close at 157.18. Chiron Corp.(NASDAQ:CHIR) jumped $6.37 to $51.75, AlliancePharmaceutical Corp. (NASDAQ:ALLP) gained $6.13 to $23.38on favorable FDA news, and Somatogen Inc. (NASDAQ:SMTG)climbed $5.50 to $32.

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