59 patients with acute leukaemia were examined to see if hypocholesterolaemia, which is commonly found in acute leukaemia, was due to the high low-density-lipoprotein (LDL)-receptor activity of leukaemic cells. LDL-receptor activity was found to be inversely correlated with plasma-cholesterol concentration. Patients with both a high LDL-receptor activity per cell and a high white-blood-cell count had the lowest cholesterol concentrations. During chemotherapy, cholesterol levels rose concomitantly with the disappearance from the peripheral blood of leukaemic cells. Hypocholesterolaemia in leukaemia and other neoplastic disorders may be due to increased LDL-receptor activity in the malignant cells. This high uptake and degradation of LDL by malignant cells could be utilised to target neoplastic cells with LDL-bound chemotherapeutic agents.