Unstable angina pectoris is a clinical syndrome characterized as a rule as rapid deterioration of angina or newly developed angina pectoris. The authors examined 30 patients with unstable angina pectoris who were admitted to hospital within 24 hours after the attack. Coronarography was performed on average after 14.6 hours. In all patients significant coronary stenoses were found. Streptokinase was administered into the coronary artery exhibiting the maximum narrowing in a total dose of 500,000 u. at a rate of 10,000 u/min. After streptokinase administration improvement of the coronarographic finding was recorded in 53% of the group, subjective improvement in 77%. Newly developed angina pectoris exhibited coronarographic improvement in 100%. Deteriorated angina improved coronarographically in 36%, subjective improvement was recorded in 68%. The authors found a significant difference (p less than 0.01) between the group of new anginas and deteriorated anginas following treatment, the coronarographic improvement being in favour of the group of fresh anginas (100% vs. 36%). The authors did not detect a significant difference between the groups when evaluating subjective improvement. In the group of deteriorated anginas more frequently subjective improvement was observed (68%) without detectable coronarographic improvement (36%). The authors verified on their own material that in more than 50% of the patients with sudden deterioration or the development of angina pectoris classified as unstable angina pectoris thrombotic narrowing can be found or even occlusion of the coronary arteries. The authors recommend therefore intravenous streptokinase administration in newly developed angina pectoris. In deterioration of angina pectoris they recommend heparin or possibly streptokinase as the drug of choice.