A technique for using 99Tcm-methoxyisobutylisonitrile (MIBI) to evaluate leg muscle perfusion in the assessment of peripheral vascular disease (PVD) is described and evaluated. The uptake of MIBI in muscle groups is quantified and normalized to whole body activity. Eleven patients with PVD undergoing angiography and nine controls were studied. There was a significant difference in MIBI uptake in the calf (P less than 0.000 01) and thigh (P less than 0.0001) between the two groups on exercise. The technique has a sensitivity of 91% and specificity of 94% for the diagnosis of PVD. The technique can also effectively evauate the severity of disease as shown by significant correlations between exercise calf flow and angiographic severity (P less than 0.05) and Doppler ankle/arm pressure measurements (P less than 0.0005). Single photon emission tomography (SPET) of the calves was also performed in five controls and five patients with PVD. Uptake was significantly reduced in all muscle areas in patients with PVD and, amongst those with PVD, uptake was lower in muscle groups by occluded arteries. The potential role of 99Tcm-MIBI in the assessment of PVD and its advantages over other methods of assessment are discussed.