Human alveolar macrophages were recovered by bronchoalveolar lavage and superoxide anion (O2-) generation from the macrophages were measured by 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo[1,2-a]pyrazin++ +-3-one (MCLA)-dependent luminescence. Addition of 0.5 mumol/l MCLA and a stimulatory agent, such as phorbol myristate acetate (PMA) and N-formyl-methionyl-leucyl-phenylalanine (fMLP), to a suspension of the cells caused a marked luminescence which was inhibited by 0.5 mumol/l superoxide dismutase (SOD). The maximal luminescence intensity was dependent upon the number of the cells. Azelastine (A-5610, CAS 58581-89-8) significantly inhibited the O2- generation from the activated macrophages in a dose-dependent manner. However, the other antiallergic drugs, such as ketotifen, disodium cromoglycate and others showed little effects on the O2- generation from the activated human alveolar macrophages.