Prostaglandin H synthases or cyclooxygenases 1 (PGHS-1) and 2 (PGHS-2) catalyze the conversion of arachidonic acid to prostaglandin endoperoxides, leading to the formation of prostaglandin and thromboxane mediators of inflammation. The expression of these enzymes in the respiratory epithelium has not been determined, although they may be relevant to the pathophysiology of inflammatory disorders such as asthma and chronic bronchitis (CB). We studied PGHS-1 and PGHS-2 immunoreactivity in bronchial biopsies obtained from 22 patients with chronic stable asthma, seven patients with CB, and 12 normal subjects. Both types of PGHS were mainly expressed in the epithelium (basal and ciliated cells), and PGHS-1 and PGHS-2 were found in 21 of 41 and 34 of 41 biopsies, respectively. We did not find any differences in PGHS expression between the patient populations. There were no correlations between any of the clinical parameters studied or the pathologic patterns and the presence and characteristics of the PGHS immunoreactivities. Thus, both PGHS enzymes are expressed in normal human respiratory epithelium and are not quantitatively upregulated in the main bronchi in stable asthma and CB.