Fig. 1. (A ) Abnormal (positive) response to 3% halothane. Each small box represents 0.1 g tension. The contracture response in this case is 1.6 g. A normal response to 3% halothane is a contracture up to 0.7 g. After exposure to halothane, 32 mm caffeine is added to the bath to determine maximal response. (B ) Abnormal (positive) response to caffeine. Caffeine exposure is to 0.5, 1.0, 2.0, 4.0, 8.0, and 32 mm for 4 min. A contracture of greater than 0.3 g to 2 mm caffeine or less indicates susceptibility.