Molsidomine, a new venous vasodilator, was studied in 40 cases of stable angina by ergometric stress testing. 1. In 10 patients, one hour after 2 mg molsidomine sublingually, the work inducing a 1 mm ST depression (WST 1) increased by 94% (p less than 0,05), the total work by 52% (p less than 0,005) and the maximum ST depression (ST max) fell by 45% (p less than 0,01). Resting heart rate was unchanged. There was a mild fall in systemic blood pressure. 2. Molsidomine had a significant synergic effect in 3 groups of 10 patients on betablocker therapy but with ischaemic changes on exercise: a) Molsidomine 1 mg sublingually increased WST 1 by 36% (p less than 0,05); at a 2 mg dosage, by 55% (p less than 0,001). ST max decreased from 2,4 +/- 0,4 mm to 1,3 +/- 0,3 (p less than 0,005) and 1,2 +/- 0,33 (p less than 0,001) respectively. The maximal effect was obtained with 1 mg in 5 out of 10 patients. b) One and three hours after 2 mg Molsidomine sublingually or orally: WST 1 increased from 97% to 110% (p less than 0,005): ST max decreased in similar proportions (p less than 0,005). c) 2 mg Molsidomine and 230 mg isosorbide dinitrate orally were compared after two hours: WST 1 increased by 130% after Molsidomine (p less than 0,005) and by 112% after isosorbide (p less than 0,005). ST max decreased in similar proportions (p less than 0,005). The blood pressure fell less with molsidomine. Molsidomine appeared to be better tolerated than isosorbide. (5 cases of mild headache in 40 patients compared to 4 cases out of 10 patients). The results of a preliminary clinical trial are reported. The association of molsidomine (2 mg per os three times daily) reduced the number of anginal attacks by over 50% in 16 out of 17 patients inadequately controlled by betablockade alone. 3 patients complained of headache at the onset of therapy. The efficacity was comparable and the tolerance better than in 28 patients with isosorbide dinitrate and betablockade, and in 10 patients with nifedipine and betablockade. In conclusion, molsidomine is a venous vasodilator with useful pharmacokinetic properties. It seems to be effective and well tolerated in the treatment of angina whether used alone or in association with betablockers.