Cyclooxygenase metabolites of arachidonic acid are thought to play an important role in the regulation of diverse physiological functions in the lung. Although the concentration of these metabolites required to have effects is several orders of magnitude greater than the concentration of these mediators in the blood, it has been postulated that local concentrations within tissues are much higher. In a direct test of this hypothesis, the concentrations of the cyclooxygenase products of arachidonic acid including prostaglandin (PG) E, PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane B2, were measured in a specialized tissue compartment, the epithelial surface of the lower respiratory tract. The concentration of these mediators within this compartment was 50- to 80-fold greater than concurrent blood levels and are sufficient to likely have physiological effects. Thus the epithelial surface of the lower respiratory tract represents a specialized compartment with high local levels of cyclooxygenase products of arachidonic acid.