In all patients who received streptokinase infusion for strongly suspected acute myocardial infarction in 1 hospital during 1989 to 1990, the occurrence of hypotension during infusion is described and related to prognosis. In 54% of patients, the β blocker metoprolol was simultaneously administered intravenously. The median systolic blood pressure (BP) before infusion was 135 mm Hg, and the median value for the lowest systolic BP recorded during infusion was 100 mm Hg (p < 0.001). A positive correlation between systolic BP before streptokinase and the lowest systolic BP during infusion was found (r = 0.53; p < 0.001). Among patients administered streptokinase and metoprolol, 23% had systolic BP < 90 mm Hg, and 12% had <80 mm Hg at any time during infusion; corresponding values for patients administered streptokinase only were 47 and 30%, respectively. Patients with the lowest systolic BP < 80 mm Hg during infusion had a mortality during the first 2 weeks of 22 vs 11% for those with between 80 and 100 mm Hg, and 8% for those with >100 mm Hg (p < 0.001). However, in a multivariate analysis the systolic BP before infusion rather than the lowest systolic BP during infusion was independently associated with death. It is concluded that although patients with low systolic BP during streptokinase infusion have a high mortality, the level of systolic BP before infusion is more strongly associated with the outcome. Simultaneous use of intravenous β blockade does not increase the occurrence of hypotension during streptokinase infusion.