Using photography of the fundus oculi the eyeground of 186 patients with histologically different forms of nephritis, 68 patients with essential hypertension and 10 patients with renovascular hypertension was investigated and evaluated. The fundal lesions were classified according to the grades recommended by WHO. Although in many individual cases the duration of the disease was short and the patients were young, the eyeground changes in renal hypertension were notably severe. Taking as basis comparable pressure rises, marked signs of fundus hypertonicus malignus were particularly frequent in primary and secondary hypertension with focal segmental sclerosis and membranoproliferative glomerulonephritis, whereas in essential hypertension non-malignant fundus hypertonicus predominated. The eyeground findings deteriorated further with impairment of renal function. Owing to the high incidence of severe fundal lesions in renal hypertension the eyeground of these patients should be examined and the hypertension treated accordingly even when the rise in blood pressure is relatively mild (less than 180/100 mm Hg).