Although a number of markers of successful coronary thrombolysis have been proposed, only a few of these have the two necessary features of a clinically useful marker: (1) widespread early availability and (2) good predictive value. The reduction in ST-segment elevation on the standard 12 lead electrocardiogram 1-4 h after initiation of thrombolysis may be the simplest and most useful clinical 'tool' to gauge the effectiveness of thrombolytic therapy. The predictive value of this single marker might be further improved by combining it with assessment of the rate of increase of serum myoglobin and of troponin T, provided these determinations were rapidly available.