In a group of 36 untreated patients with mild-to-moderate essential hypertension (office systolic blood pressure [SBP] 160 +/- 3.4 mm Hg, office diastolic blood pressure [DBP], 102 +/- 1.5 mm Hg), 24-hour ambulatory blood pressure monitoring, and determination of left ventricular (LV) mass index according to the formula of Devereux were performed. After an overnight fast, blood samples were taken for the determination of serum aldosterone levels and plasma renin activity. Urinary catecholamine concentrations were assayed from 24-hour urine collections. Left ventricular mass index (143.7 +/- 8 g/m2) did not correlate significantly with either office SBP or office DBP. The correlation of LV mass index with mean 24-hour SBP (145 +/- 3 mm Hg) was statistically significant: r = 0.395, p = 0.026. However, the best correlation was obtained with mean 24-hour DBP (90 +/- 3 mm Hg) with r = 0.499 (p = 0.004). Urinary catecholamine levels did not correlate with LV mass index. In addition, LV mass index correlated significantly with plasma renin activity (r = 0.346, p = 0.050) and serum aldosterone levels (r = 0.559, p = 0.0009). There was a strongly significant correlation between LV mass index and serum aldosterone levels even after adjustment for mean 24-hour SBP (r = 0.496, p = 0.005) and DBP (r = 0.514, p = 0.004). These results demonstrate that ambulatory blood pressure determinations but not office blood pressure parameters correlate well with left ventricular hypertrophy in essential hypertension. Nonhemodynamic factors are important determinants of left ventricular mass as well.(ABSTRACT TRUNCATED AT 250 WORDS)