Cyclooxygenase (COX) 1 and 2 are two isoforms of a crucial enzyme in the metabolism of arachidonic acid to prostaglandins, thromboxanes and prostacyclin. It is now clear that COX-1 is expressed in the majority of cells constitutively, and COX-2 appears after stimulation. The role of cyclooxygenase expression in the pathophysiology of the airways has not been elucidated. In this study we aimed to compare cyclooxygenase expression in nasal polyps removed from well-defined atopic and nonatopic subjects. Monoclonal antibodies against COX-total (detecting both COX-1 and COX-2 epitopes) and anti-COX-2 combined with peroxidase-antiperoxidase (PAP) visualizing system were used to assess COX-total and COX-2 expression in cryostat sections of nasal polyps from both groups of patients. Chromotrope R2 or toluidine blue staining were used to detect the presence of eosinophils and mast cells, respectively. We demonstrated that cryostat sections of nasal polyps from both groups of patients revealed COX-total and COX-2 expression with similar intensity. There were no significant differences in distribution of COX-total or COX-2 immunoreactivity in nasal polyps tissue between atopic and nonatopic group. No correlation between density of cells expressing COX-2 and the number of mast cells and eosinophils was found. Our data indicate that COX-2 is expressed in nasal polyps from both atopic and nonatopic patients.