Among the many factors that have been implicated in the pathogenesis of myocardial hypertrophy is a sodium effect. In the present study, the influence of dietary sodium, estimated by 24-h natriuresis, on left ventricular mass was assessed in 41 patients with mild essential hypertension who had never been treated. Posterior wall thickness and left ventricular mass, but not left ventricular internal diameter were directly correlated with 24-h natriuresis (r = 0.47 and 0.46; P less than 0.02 and 0.002, respectively). Stepwise multiple regression analysis confirmed that 24-h natriuresis was a determinant of left ventricular mass independently of sex, age, body weight, blood pressure and the duration of hypertension. These results suggest that dietary sodium may play a role in modulating left ventricular mass in untreated hypertensives.