OBJECTIVE To assess sodium-lithium countertransport (SLC) activity and erythrocyte sodium (ENa) levels in black (Nigerian) hypertensive (HT) patients, normotensive (NT) offspring of hypertensive parents and normotensive offspring of normotensive parents, and to determine if increased SLC activity is related to a familial predisposition to hypertension in black subjects as in Caucasians. METHODS The study was done using 60 Nigerian subjects of Edo ethnic origin in three groups of 20 each: (a) untreated new HT patients at the University Teaching Hospital, Benin City; (b) NT children of hypertensive parents (NTHT) traced home and matched for age, sex and body mass index (BMI) with (c) NT children of NT parents (NTNT). SLC activity was measured using a modified method of Canessa et al 1980 and ENa assessed by flame photometry. RESULTS SLC was markedly higher in both HT patients and NTHT subjects than the NTNT subjects. The values were 0.351+/-0.011 vs 0.199+/-0.014 mmol Li/rbc (P < 0.0001) and 0.347+/-0.020 vs 0.199+/-0.014 mmol Li/rbc/hr (P < 0.0001), respectively. The values were not different between the HT and the NTHT group (P > 0.05). ENa was higher in the HT group than both NT groups which were similar. Values were 10.55+/-0.46 (HT) vs 7.78+/-0.62 (NTHT) (P < 0.0001) and 10.55+/-0.46 (HT) vs 8.62+/-0.47 mmol/L (P < 0.0001). There were no correlations between either SLC activity or ENa and any of the other measured variables such as age or BMT. CONCLUSIONS SLC activity was elevated in normotensive children of hypertensive subjects to a similar degree as hypertensive patients and in a pattern reminiscent of that seen in Caucasians. SLC activity may thus be associated with a familial predisposition to hypertension in black subjects as in their Caucasian counterparts.