To evaluate the utility of rest-injected 201Tl initial and delayed images for assessing the viability of severe asynergic regions, we studied 17 patients with apparently prior infarcted myocardium in combination with 99mTc ventriculography before and after revascularization. In 51 regions with severe asynergy, the percent 201Tl uptake was calculated as the ratio of counts on the segment with asynergy to the maximum counts on the normal segment. Eleven of 14 regions with resting 201Tl redistribution (Group 1) had improved wall motion after revascularization. However, 14 of 37 regions without redistribution also improved (Group 2). Twenty-three regions without redistribution or improved wall motion after revascularization (Group 3) had lower regional 201Tl uptake on their delayed images than those in Groups 1 and 2. Moreover, the initial regional uptake of Group 2 was higher than that of Group 3. These results suggest that redistribution on rest-injected 201Tl scans indicates reversibility of severely asynergic myocardium and that high 201Tl uptake in regions without redistribution may predict improvement in wall motion after revascularization. We conclude that 201Tl uptake may be useful as a marker of viability of severe asynergic regions before revascularization.