A patient is reported with drug-resistant familial hypercholesterolaemia in whom serum cholesterol fell after the onset of gallbladder cancer with intraperitoneal invasion. Cancer cells were obtained from ascitic fluid and a cultured cell line established. Incubation of the culture medium of these cells with skin fibroblasts from the patient and from normal subjects increased low-density lipoprotein (LDL) receptor activity in a dose-dependent manner. These results show that gallbladder cancer cells from this patient secrete a substance that stimulates LDL receptor activity. This substance may have contributed towards reduction of serum cholesterol.