The effect of four weeks of treatment with beclomethasone dipropionate (BDP, 500 micrograms twice daily) on the bronchial responsiveness to propranolol was examined in 16 patients with mild asthma in a placebo-controlled, double-blind crossover study. Propranolol was inhaled in doubling concentrations and the results were expressed as the cumulative dose producing a 20 percent fall in FEV1 (PC20). After four weeks of treatment with BDP, the mean FEV1 increased from 82.0 percent predicted to 88.1 percent predicted. The difference was significant (p less than 0.001). Treatment with BDP did not significantly change the responsiveness to propranolol, the geometric mean PC20 being 3.17 mg/ml before and 3.64 mg/ml after BDP treatment. The recovery of FEV1 was faster after 60 minutes of BDP treatment in comparison with placebo treatment (beyond 90 minutes). This study suggests that BDP treatment is unable to reduce bronchial responsiveness to propranolol but can accelerate the recovery of bronchoconstriction induced by propranolol in asthmatic patients.