Platelet-activating factor (PAF) has been reported to play a role in allergy and inflammatory reactions but its role in the pathogenesis of nasal polyps remains unclear. In this study, we examined both PAF and peptide leukotrienes (peptLTs) in individual preparations from nasal polyps. The amounts of PAF were much greater than those of peptLTs in all preparations. Nasal polyps were divided into two groups according to the severity of eosinophil infiltration: a severe group (eosinophil count > or = 50/mm2) and a mild group (eosinophil count < 50/mm2). The amounts of PAF in the nasal polyps were significantly higher in the severe group than in the mild group (p < 0.01). PAF activity correlated with tissue eosinophilia and polyps obtained from patients with aspirin-sensitive asthma contained relatively large amounts of PAF, with enriched infiltration of eosinophils.