We sought in this study to examine the effects of diurnal blood pressure variations upon common carotid artery (CCA) elasticity in selected subjects with uncomplicated moderate essential hypertension. Towards this end, 174 non-smoker subjects with stage I-II essential hypertension and without diabetes mellitus, left ventricular hypertrophy and carotid atherosclerosis, were classified as dippers and non-dippers according to the diurnal variation of >10% between mean daytime and night-time systolic and diastolic blood pressure (BP) in 24-h non-invasive ambulatory BP monitoring. CCA distensibility was derived by a combination of surface ultrasonographic data and simultaneous BP measurements at the brachial artery. The dippers and non-dippers were similar with respect to demographic characteristics. Non-dippers had significantly greater office systolic BP, 24-h systolic BP and ambulatory pulse pressure (PP) and significantly less (daytime-night-time) systolic and diastolic BP fall (by 16 mm Hg and 11 mm Hg respectively, P< 0.0001) compared to dippers. CCA distensibility was significantly reduced in non-dippers compared to dippers (by 0.89 dyne(-1)/cm(2/)10(-6), P < 0.05). Multiple linear regression analysis identified patient age and ambulatory PP as significant predictors of the CCA elasticity index. When patient age, 24-h systolic and diastolic BP were used as covariates in an analysis of covariance, the difference of CCA elasticity between dippers and non-dippers ceased to reach statistical significance. In contrast, when patient age, ambulatory PP, systolic (daytime-night-time) BP fall and diastolic (daytime-night-time) BP fall were used as covariates, the difference of CCA distensibility between dippers and non-dippers continued to be statistically significant. In conclusion, the excessive impairment of CCA elastic properties in non-dippers compared to dippers hypertensive seems to be ascribed to the increased of total 24-h haemodynamic load and not to the circadian pattern of BP. Journal of Human Hypertension (2000) 14, 813-818