163 patients aged from 27 to 70 years (mean 52 +/- 10 years), including 152 men and 11 women, received a thrombolytic treatment within the first 6 hours (mean 192 +/- 73 mn) of a myocardial infarction. 61 patients received streptokinase (SK) intravenously (group 1), 64 patients, single-chain rt-PA (group 2), 11 patients, two-chain rt-PA (group 3), 11 patients, rt-PA followed by intracoronary streptokinase (group 4), and 16 patients, acyl enzyme (group 5). In addition, all patients had heparin and 86 (53%) had aspirin. Immediately after thrombolysis, coronary arteriography was performed in 95 patients (58%), and this was followed by transluminal angioplasty in 49 of them (30%). The infarction was either anterior (n = 81) or inferior (n = 78) or lateral (n = 4). No fatal or neurological bleeding occurred. 17 haemorrhagic complications were observed; 5 of these (3%) were severe, requiring blood transfusion and, in 1 case, surgery; 12 were significant (7.4%) and produced changes in haematocrit. Nine of the 17 haemorrhages were associated with catheterization and localized to the site of arterial puncture. Severe bleeding occurred in patients treated with intravenous SK (3/61) or with rt-PA followed by intracoronary SK (2/11). There was a significant difference in the incidence of spontaneous bleeding between the SK group (4/61) and the single-chain rt-PA group (0/64; p less than 0.05). In the latter group, the minimum fibrinogen level was lower in patients who had a haemorrhagic complication.(ABSTRACT TRUNCATED AT 250 WORDS)