The aim of the present study was to investigate the relaxant effects of selective III, IV and nonselective phosphodiesterase inhibitors, e.g. amrinone, rolipram and theophylline, respectively, on isolated tracheal preparations in streptozotocin (STZ)-diabetic rats. Six weeks before the experiments, the rats to be made diabetic were anesthetized with diethyl ether and diabetes was then induced by a single intravenous injection of STZ (65 mg kg(-1)) via the tail vein. All drugs produced concentration-dependent relaxations of tracheal preparations precontracted with 10(-6) mol/l carbachol. The responses of phosphodiesterase inhibitors were marked in the diabetic groups compared to the control group, but it was found that only amrinone responses are significantly higher in the diabetic groups. Copyright (C) 2000 S. Karger AG, Basel.