Radiographic chest findings from 57 men, aged 17 to 64, with untreated systemic arterial hypertension of varying severity were related to systemic haemodynamics, both at rest and during standardized exercise in the sitting position. The haemodynamic findings were compared with corresponding data from 59 normotensive male volunteers. In classifying the radiographic findings into four different groups, not only the heart size but also the appearance of the aorta and left ventricle were taken into account. While there was only a poor correlation between calculated heart volume and resting mean brachial artery pressure or systemic vascular resistance, the classification system used resulted in a good separation for haemodynamic functions of patients with normal chest films, those with elongated and widened aorta, and those with signs of left ventricular hypertrophy. On the other hand, there was no definite difference in the functions studied for hypertensive patients with left ventricular hypertrophy and those with, in addition, signs of left ventricular dilatation. Hypertensive men with normal chest radiographs stood out as characterized by increased heart rate and cardiac output at rest, while the systemic vascular resistance was not different from that of the controls. Already the presence of an elongated and widened aorta changed this haemodynamic pattern to that characteristic of established arterial hypertension with normal resting heart rate and cardiac output, and increased systemic vascular resistance. Considerably better information on the haemodynamic events in systemic arterial hypertension is possible to achieve with a thorough evaluation of the radiological appearance of the aorta and left ventricle, rather than with estimation of the heart size only.