Antagonism of the effects of platelet activating factor (PAF) by the ginkgolide mixture BN 52063 was assessed in a double-blind, placebo-controlled, crossover study in 6 normal subjects. Weal and flare responses to 400 ng PAF, examined 2 h after ingestion of BN 52063 (80 mg, 120 mg) were inhibited in a dose-related manner. After 120 mg the flare area was reduced by a mean 62.4% (p less than 0.005) and the weal volume by a mean 60% (p less than 0.05). Both doses of BN 52063 significantly inhibited PAF-induced platelet aggregation in platelet-rich plasma (p less than 0.001). In vitro, BN 52063 inhibited PAF-induced but not ADP-induced platelet aggregation. Thus BN 52063 seems to be an antagonist of PAF in man.