We have investigated the duration of the inhibitory effects of aspirin in eight healthy volunteers after oral administration of a single 500 mg dose. Prostaglandin E2, D2 and leukotriene C4 levels in nasal lavage fluid were measured by radioimmunoassay without purification by high performance liquid chromatography. The inhibitory effects of aspirin on eicosanoid synthesis were maximum between 1 h to 24 h, showing total recovery within 3-5 days. LTC4 synthesis was not modified by aspirin.