In a series of 175 adult renal transplant patients 59% of patients had hyperlipidemia. Hyperlipidemia in these patients was characterized by both hypercholesterolemia and hypertriglyceridemia and on lipoprotein electrophoresis was demonstrated to be a mixture of types IIa, IIb and IV hyperlipoproteinemia. Serum cholesterol and triglyceride levels could both be related to the dosage of prednisone these patients received. Serum triglyceride levels could further be correlated with obesity and negatively with the duration of graft function. The latter relationship was felt to reflect the lower dose of prednisone that was administered the longer the duration of graft function. Hypertriglyceridemia was more prevalent in the 47 transplant patients who received kidneys from cadaver donors than in the 128 patients who received kidneys from related-donors. The cadaver-donor renal transplant patients, however, were receiving a larger maintenance dose of corticosteroids and had had functioning transplants for a shorter period of time. In 17 patients followed for up to 20 wks immediately following transplantation both hypercholesterolemia and hypertriglyceridemia developed within 8 wks of transplantation and persisted for the remaining 12 wks. Both serum cholesterol and triglyceride levels in this early post-transplant phase could be related to the cumulative prednisone dosage.