The interaction between the ginkgolide BN 52021 and the effects of PAF-acether on the bronchopulmonary system of the guinea-pig was studied. In pentobarbitone or ethyl carbamate-anaesthetized animals, BN 52021 (1 mg/kg i.v. or 10 mg/kg p.o.) inhibited bronchoconstriction, the hematocrit increase and the accompanying thrombopenia and leukopenia induced by PAF-acether (33-100 ng/kg) and failed to block the bronchoconstriction produced by collagen, arachidonic acid and the tripeptide formyl-Met-Leu-Phe (FMLP). BN 52021, 3 mg/kg, reduced the bronchoconstriction induced by aerosolized PAF-acether. BN 52021, 300 microM, also inhibited the superoxide production by PAF-acether-stimulated alveolar macrophages and failed to reduce the same effects when triggered by FMLP (0.01-1 microM). BN 52021 blocked the formation of thromboxane-triggered by PAF-acether (100 ng) injected into perfused lung, under conditions where the effects of arachidonic acid where not modified. Finally, pretreatment of parenchyma lung strips with BN 52021 (100 microM) partially inhibited the contraction induced by PAF-acether (0.1 microM) and suppressed the accompanying release of thromboxane. BN 52021 is a selective antagonist of the effects of PAF-acether on the bronchopulmonary system and on circulating blood cells of the guinea-pig.