104 adult patients with predominantly extrinsic perennial asthma who were maintained on bronchodilator or glucocorticoid therapy, were entered into a one-year open study designed to evaluate the efficacy, safety and acceptability of picumast dihydrochloride (3,4-dimethyl-7-[4-(4-chlorobenzyl)piperazine-1-yl]propoxycoumarin dihydrochloride) (2 mg twice daily). 74 patients completed the 12-month treatment period and a further 18 (total 92) were followed up for at least 2 months. Adverse drug reactions were reported in 14 patients and 5 of them were withdrawn from the trial for only non serious reactions. 12 patients were excluded from the analysis of efficacy because they dropped out early and no sufficient data were available for a judgement. Although this was an open study, analysis of diary card measurements and clinical assessments indicate that picumast dihydrochloride could represent a new and effective prophylactic therapy in the long-term management of bronchial asthma. Picumast dihydrochloride improved forced expiratory volume in 1 s (FEV1), peak flow and subjective asthmatic symptoms in 51%, 64% and 70% of the patients, respectively. 92% of those who participated in this study were willing to take the study drug again.