The preparation Actilyse--a tissue plasminogen activator prepared by recombination--is an effective fibrinolytic drug. The authors recorded in a group of 33 patients reperfusion in 91%, evaluated on the basis of indirect criteria. In a group of 18 patients treated with streptokinase reperfusion was achieved in 74%. Based on changes of CK and CK-MB values--an earlier rise of values following Actilyse administration and conversely their more marked increase during subsequent sampling after streptokinase administration--it may be assumed that earlier dissolution of the thrombus in the coronary artery occurs after Actilyse administration, as compared with streptokinase. It may be thus assumed that there is also a smaller necrotic focus after Actilyse treatment, as compared with streptokinase. Early re-occlusion--according to indirect indicators--occurred in 8.6% in the Actilyse treated groups, as compared with 5.9% in the streptokinase treated group. The fibrinogen values decline in the Actilyse group to 40% and in the streptokinase group to 28%. Later enhanced new formation of fibrinogen occurs and the fibrinogen values rise to 160% in the Actilyse treated group and to 250% of the initial value in the streptokinase treated group. The elevated fibrinogen value, as compared with the baseline value, persists for the 12 days of the follow-up. No severe spontaneous haemorrhage was recorded, haemorrhagic manifestations were associated with blood sampling and i.v. administration of drugs only. The necessity to administer blood was due to a complication during puncture of the subclavian vein in one patient.(ABSTRACT TRUNCATED AT 250 WORDS)