A method for quantifying the uptake of Tc-99m-labeled phosphate complexes in the femoral head has been clinically evaluated, being used specifically for studying the uptake of these bone-seeking agents in Perthes' disease. The analysis depends on the selection, by computer program, of a reliable reference area in the femoral shaft, which is then compared with the mean uptake from each femoral head. The femoral-head activity is then represented as an uptake ratio. These ratios, together with a fixed contour representing the uptake in the femoral-head regions, provide more clinical information than the radiograph or scintiphoto, particularly in the early stages of unilateral or bilateral femoral-head disease and during followup. No correlation has been found between these ratios and qualitative techniques for assessing Perthes' disease by radiograph. From the quantitative data so far obtained it is clear that osteotomy reduces the vascularity of the femoral head, and in certain cases this reduction persists for some years. Tc-99m-labeled diphosphonate compounds were used in more recent studies, and a significant increase in sensitivity was obtained, compared with earlier polyphosphate data.