Several methods have been suggested for risk stratification of patients with unstable coronary syndromes. However, most of these are applied several days after hospital admission. In this study we investigated the prognostic value of continuous ST-segment and QRS vector monitoring with computerized vectorcardiography (VCG), serial measurements of creatine kinase isoenzyme MB (CK-MB), predischarge stress testing and baseline data in patients with unstable angina pectoris or non-Q-wave infarction. During the 24 h VCG monitoring, 56 (29%) of the 195 patients had ST-vector magnitude (ST-VM) episodes of ischaemia. Seventy-four (38%) patients had a peak CK-MB value of 6 micrograms/l or higher during the 48 h sampling period. Several discrete variables were associated with death or non-fatal infarction at 1 year of follow-up in an univariate analysis. Among these were age > or = 65 years, female sex, St depression on the admission ECG or VCG monitoring, and elevated CK-MB levels, but neither the occurrence, duration nor intensity of chest pain. With Cox's proportional hazards regression analysis, ST-VM episodes on VCG monitoring were identified as independent markers of the risk of death (P = 0.013), death or non-fatal infarction (P = 0.035) and death, non-fatal infarction, unstable angina during the first year, or revascularization before hospital discharge (P = 0.005). VCG monitoring of ischaemia provides independent prognostic information in unstable angina. High-risk patients can easily be identified within 24 h of hospital admission. Whether early intervention based on these criteria will result in improved prognosis remains to be shown in future studies.