In a random house-to-house study of 18000 urban Zulus the overall prevalence of essential hypertension was %25 (female 27%; males 23%). Women between the ages of 35 and 40 years had a higher prevalence than men. The mean arterial pressure according to age and sex was not as high as in the American Negro, West Indian or Nigerian, but certainly higher than in most Caucasian populations. The mean arterial pressure rose with age, showing a greater rise in systolic than in diastolic blood pressure. More effective screening and therapeutic programmes should be initiated in Blacks, since this study showed that 90% of the subjects who had hypertension were undiagnosed, undetected or inadequately treated.