Long-term administration of macrolide antibiotics reduced the number of lymphocytes in bronchoalveolar lavage fluid in patients with chronic airway inflammatory disease. To evaluate the inflammatory activity of macrolides, their effect on apoptosis of activated lymphocytes isolated from human peripheral blood was compared with that of other antibiotics. Macrolides, including clarithromycin and azithromycin, at a final concentration of 100 microg/ml accelerated apoptosis of activated lymphocytes, while other antibiotics such as fosfomycin sodium, beta-lactams--ceftazidime, piperacillin sodium and biapenem, and a quinolone, ofloxacin, did not cause significant induction of apoptosis. Our results suggest that 14- or 15-membered ring macrolides are specifically involved in the augmentation of apoptosis of activated lymphocytes, and this may be of value therapeutically for chronic airway diseases.