Erythrocyte sodium-lithium countertransport was measured in normolipidaemic and hyperlipidaemic hypertensive patients, hyperlipidaemic normotensive patients and normal controls. Hypertension and hyperlipidaemia were each independently associated with raised sodium-lithium countertransport (by analysis of variance, P less than 0.01 and P less than 0.01). The effects were additive so that hyperlipidaemia could not explain raised sodium-lithium countertransport in hypertension. In hyperlipidaemic hypertensive patients, levels of plasma cholesterol, triglycerides, low-density lipoprotein (LDL) cholesterol and very-low-density lipoprotein (VLDL) cholesterol were increased, and high-density lipoprotein (HDL) cholesterol was reduced. Of these patients, 73.3% had a known family history of hypertension. Their normotensive first degree relatives were studied, and 48% of these also had raised sodium-lithium countertransport and abnormal plasma lipids (raised cholesterol, triglycerides and LDL cholesterol, and reduced HDL cholesterol). Relatives with normal sodium-lithium countertransport had normal lipids. Therefore, raised sodium-lithium countertransport was associated with the inheritance of both hypertension and hyperlipidaemia, and this could explain why raised sodium-lithium countertransport has been associated with a family history of both hypertension and associated cardiovascular disease.