1. Continuous intra-arterial ambulatory monitoring of blood pressure was recorded in 46 patients with mild to moderate hypertension under standardized conditions. M-mode echocardiography was performed after recording and left ventricular mass index calculated by standard formulae. 2. Systolic blood pressure from continuous recording was significantly correlated with left ventricular mass index (mean 24 h: r = 0.543, n = 45, P < 0.001). Diastolic blood pressure exhibited a weaker but still significant correlation with left ventricular mass index (mean 24 h: r = 0.318, n = 45, P < 0.05). Casual systolic blood pressure was significantly correlated with left ventricular mass index ( r = 0.476, n = 46, P < 0.001) but casual diastolic blood pressure did not correlate with left ventricular mass index ( r = 0.245, n = 46). Awake blood pressure variability, age, resting plasma renin activity and resting plasma noradranaline levels did not have a significant correlation with left ventricular mass index. 3. Nine patients were treated for 16 weeks with once-daily timolol and repeat ambulatory monitoring and M-mode echocardiography was performed with the same protocol. 4. Once-daily timolol provided good 24 h control of blood pressure and repeat echocardiography showed a reduction in left ventricular mass index in that group of patients ( t = 2.59, P < 0.05).

1. Ambulatory blood pressure recordings were made over a 48 h period on six hypertensive patients. The conditions of study were standardized, particularly with regard to physical activity, and during one period of each day the patients were randomly allocated to be active or inactive. 2. Results show that blood pressure was highest during physical activity and lowest during sleep. There was no significant difference between the arterial pressures measured during the same physical activities carried out at the same time each day. However, during the same time on consecutive days when activity was randomized, there was a significant difference between the pressure recordings during physical activity compared with those during inactivity. Heart rate changes showed a similar trend during the randomized period. 3. Physical activity and sleep have a profound effect on continuous arterial blood pressure recordings and these are independent of time alone. These observations should be taken into account when using this ambulatory system to assess hypotensive therapy.