1 YM-26734 [4-(3,5-didodecanoyl-2,4,6-trihydroxyphenyl)-7-hydroxy-2-(4-hydroxyphenyl)chroman] dosedependently inhibited the activities of extracellular phospholipase A2 (PLA2): rabbit platelet-derived group II and porcine pancreas-derived group I PLA2, with ICs values of 0.085 (0.056-0.129, n = 5) and 6.8 (5.0-9.6, n = 5) ylM, respectively. 2 In contrast, YM-26734 did not reduce the activity of intracellular PLA2 prepared from mouse macrophages, which preferentially hydrolyzed arachidonoyl phospholipids at concentrations up to 50SAM. YM-26734 also showed no effect against either sheep seminal vesicle cyclo-oxygenase or rat leukocyte 5-lipoxygenase. kg-', i.v.) than in the control group (0.43 ± 0.02 vs 0.59 ± 0.03 g per cavity and 3.8 ± 0.2 vs 4.9 ± 0.3 x 107 cells per cavity, respectively; n = 5). 6 These results suggest that YM-26734 is a potent and competitive inhibitor of extracellular PLA2 with selectivity for group II PLA2, and that the inhibition of group II enzymes activity may cause the suppression of inflammatory responses to TPA and carrageenin.