Peripheral vascular disease is a serious and common complication in patients with diabetes mellitus (DM). Evaluation is, conventionally, by transcutaneous oxygen tension measurements (TcpO2), although this technique has some limitations in the evaluation of tissue viability. We have evaluated a new, radiolabelled, in vivo marker of tissue hypoxia, iodoazomycinarabinoside (IAZA), by comparing TcpO2 measurements with patterns of iodine-123 IAZA uptake in ten patients (19 lower limbs) with DM and peripheral vascular disease using conventional gamma camera imaging techniques. Normal uptake patterns were seen in limbs in which normal TcpO2 measurements were obtained. Diffusely increased uptake of [123I]IAZA was seen in limbs with reduced TcpO2. Focally increased uptake was seen in ulcers or in areas of atrophic skin change. A semi-quantitative measure showed an inverse correlation between [123I]IAZA and TcpO2 values. These data suggest that tissue hypoxia can be imaged in this population of patients and that severity of disease can be assessed. A longitudinal prospective trial is now being developed.