The rate of red blood cell sodium-lithium countertransport is elevated only in a subgroup of patients with essential hypertension. We have therefore compared renal and cardiac function and morphology in two groups of hypertensive patients with high (n=23) or normal (n=22) sodium-lithium countertransport (mean±SEM: 0.61±0.10 versus 0.29±0.07 mmol/l red blood cells - hr). The two groups were similar in age, sex distribution, body mass index, smoking habit, duration of hypertension, and actual levels of untreated blood pressure. Hypertensive patients with elevated sodium-lithium countertransport activity showed elevated glomenilar filtration rate (118±2 versus 109±2 ml/min • 1.73 m2;p<0.001), albumin excretion rate (23±3 versus 14±2 /ug/min; p<0.001), larger kidney volume (250±15 versus 203±13 ml • 1.73 m2;p<0.01), lower lithium clearance rate (26.7±03 versus 28.9±03 ml/min • 1.73 m2;p<0.01), and higher total body exchangeable sodium (2,716±33 versus 2,485±41 mmol • 1.73 m2;p<0.01). Left ventricular mass index (139±6 versus 119±6 g/m2;p<0.05), relative wall thickness (0J9±0.05 versus 0.29±0.04 cm;p<0.001), and left posterior wall plus intravenrricular septum thickness (2.02±0.04 versus 1.76±0.03 cm; p<0.05) were also higher in patients with high sodium-lithium countertransport Hypertensive patients with normal sodium-lithium countertransport had renal and cardiac parameters similar to those of a normotensive control group (n=21) except for a higher glomenilar filtration rate and left ventricular mass index. Finally hypertensive patients with elevated rates of sodium-lithium countertransport had significantly higher plasma triglyceride levels and lower plasma concentrations of high density lipoprotein cholesterol. Thus renal and cardiac hypertrophy, lipid abnormalities, and altered kidney function are prominent features of hypertensive patients with higher sodium-lithium countertransport