In a study of 70 renal transplant patients, the prevalence of hyperlipidaemia eight to 28 months following transplantation was found to be 59 per cent. High density lipoprotein (HDL) cholesterol levels were normal but low-density-lipoprotein (LDL) cholesterol levels were significantly elevated compared with controls. Lipid levels, measured before and sequentially after transplantation for 22 months in 10 patients were elevated over the first six to 10 months. Thereafter the lipid values returned to normal in most patients. This change coincided with the attainment of maintenance steroid dosage (usually prednisolone 10 mg. daily; mean 12.5 mg). A diet designed to decrease cholesterol and increase polyunsaturated fat intake, resulted in a significant reduction of serum cholesterol levels but not of triglyceride values over a four week period. The results suggest that the hyperlipidaemia in the initial months after transplantation may well be related to the high dose steroid therapy during this period, and the levels of lipid return to normal once low dose maintenance therapy is attained. Lipid profiles and levels in the first eight to 12 months are variable and should not form the basis for therapy or assessment. Dietary modification alone is unlikely to be an effective form of treatment of severe hyperlipidaemia in these patients.