Hemodynamic (CATELIX/DF32P system) assessment of circulatory disturbances in idiopathic avascular necrosis (12 femoral heads of 10 patients), demonstrate that vascularity in the necrotic portion was less than 15 per cent (mean, 9%) of normal levels. In 2 cases reassessed after surgery, the recovery of vascularity was to 98 per cent. The vascularity in the translucent portion was fairly well maintained at 50 to 139 per cent. From a histological point of view, vascularity of less than 15 per cent is indicative of ischemia and necrosis of the bone. Hemodynamic methods demonstrate the presence of focal necrosis, long before there are obvious roentgenological abnormalities. The CATELIX/DF32P system is better than the G-M probe/32P system in some respects and is now readily available.