Computerised apex- and echocardiography was used to study left ventricular dimensions and function in 13 patients with untreated malignant hypertension and eight with severe benign hypertension. All patients had normal left ventricular cavity dimensions. Five benign hypertensives and malignant hypertensives with a previous history of hypertension had significant thickening of the septum and posterior wall. In eight malignant hypertensives without a previous history wall thicknesses were normal. The absence of ventricular hypertrophy in some cases of malignant hypertension suggests that it is sometimes of rapid onset and not preceded by a non-malignant phase. although fractional shortening and peak Vcf were normal in all the hypertensives, diastolic left ventricular function was frequently abnormal with delayed mitral valve opening, reduced peak rate of filling, and outward endocardial motion during isovolumic relaxation. Malignant hypertensives showed a cavity shape change during isovolumic contraction, and in those without a previous history the aortic second heart sound occurred earlier. The abnormalities of function are probably the result of a combination of factors including pressure overload, abnormal myocardial properties, and myocardial ischaemia, either regional or generalized and secondary to arteriolitis.