We have compared stress-redistribution and delayed rest thallium-201 with rest technetium-99m methoxyisobutylisonitrile (MIBI) tomograms in order to compare the tracers for the assessment of myocardial viability and to validate a rapid protocol combining the two tracers. We studied 30 consecutive patients with known or suspected coronary artery disease [group 1: 16 with normal left ventricular function, mean left ventricular ejection fraction (LVEF) 55%, SD 6%; group 2: 14 with abnormal function, mean LVEF 28%, SD 8%]. 201Tl was injected during infusion of adenosine followed by acquisition of conventional stress and redistribution tomograms. On a separate day, 201Tl was injected at rest with imaging 4 h later. 99mTc-MIBI was then given at rest and imaging was performed. Three images were compared: redistribution 201Tl, rest 201Tl, and rest 99mTc-MIBI. Tracer activity was classified visually and quantitatively in nine segments and segments with > 50% activity were defined as containing clinically significant viable myocardium. Mean (+/- SD) global tracer uptake as a percentage of maximum was similar in group 1 (rest 201Tl 69% +/- 12%, redistribution 201Tl 69% +/- 15%, rest 99mTc-MIBI 70% +/- 13%, ANOVA P > 0.05), but in group 2 mean tracer uptake was significantly greater in the rest 201Tl images (59% +/- 16%) than in redistribution 201Tl images (53% +/- 17%) or rest 99mTc-MIBI images (53% +/- 19%) (ANOVA P = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)