The effect of antiallergic agents (DSCG) (disodium cromoglycate, ketotifen, and ibudilast) and beclomethasone dipropionate inhaler (BDI) on bronchial hyperresponsiveness to histamine inhalation was retrospectively assessed in 72 asthmatic patients with more than a year's duration of the disease. Decrease in bronchial hyperresponsiveness to histamine was observed in 10 out of the 33 (30%) antiallergic-agents-treated patients (group A, mean duration = 7.8 months), in 12 of 19 (63.2%) BDI-treated patients (group B, 6.2 months), but only 2 of the 20 (10%) control patients (group C, 7.8 months). Improvement of histamine PC20 was from 310 to 597 micrograms/ml (P < 0.01) in group A, from 308 to 1622 micrograms/ml (P < 0.0005) in group B, and from 575 to 525 micrograms/ml (NS) in group C. A significant decrease in the peripheral eosinophil count was observed only in group B. The improvement in bronchial hyperresponsiveness was parallel with that of asthmatic symptoms; the percentage of patients becoming symptom-free rose from 12 to 42%, 5 to 89%, and 5 to 20% in groups A, B, and C, respectively. Out of 11 unimproved patients in group A, 7 showed a significant improvement in their histamine PC20 by BDI treatment (mean PC20: 311-->1828 micrograms/ml). These results suggest that BDI might be more effective than antiallergic agents in the treatment of patients with long-standing bronchial asthma.