201Tl perfusion scintigraphy of the legs was evaluated to define intermittent claudication quantitatively, based on Sapirstein's indicator fractionation principle. After intravenous injection of 201Tl with or without exercise, the distribution of the radiotracer throughout the body was obtained using the whole blood scanner. Regional blood flow of cardiac output for three segments of the leg was estimated as a regional fractional uptake (rFU) distributed in these segments compared with the whole body distribution. The validity of the principle was confirmed by a comparative study with 99mTc-MAA (r = 0.979). Normal rFUs (%) for each section at rest and after stress, respectively, were 5.49 +/- 0.69 and 19.40 +/- 2.04 (whole leg); 3.57 +/- 0.49 and 12.26 +/- 1.91 (thigh); 1.59 +/- 0.34 and 6.58 +/- 0.61 (calf). The rates of rFU change from the state of rest to stress (delta rFU) in normals were 3.41 +/- 0.45 (whole leg), 3.44 +/- 0.61 (thigh), and 4.30 +/- 1.03 (calf). Although rFU was within normal limits in patients with arteriosclerosis obliterans (ASO) and thromboangitis obliterans (TAO), delta rFU of the whole leg was significantly decreased from the normal value of 3.41 +/- 0.45 to 1.95 +/- 0.40 for ASO (P less than 0.001) and 1.82 +/- 0.47 for TAO (P less than 0.001). A defect or decreased activity on the stress scintigraph was well correlated with the angiographic findings.