BN-52021 preserves "in vitro" the actively sensitized guinea-pig heart from the immunological reaction. This ginkgolide reduces mediator release (histamine, thromboxane-A2 and slow reacting substance of anaphylaxis) in a dose-dependent manner, particularly that of histamine. These results evidence either an important role for PAF in guinea pig anaphylaxis or a wider spectrum of activity for BN-52021.