A comprehensive clinical and immunological examination was carried out in 32 patients with a condition diagnosed as kidney tumour. The immune status was investigated by in vivo determination of the delayed-type immune reaction by means of cutaneous reactions to primary and recall antigens. The possibilities of differential diagnosis and the value of the individual examinations are discussed from the clinical point of view. Particular importance is attached to angiography and it is pointed out that the first step should always be standard radiography of the aorta suspected because of the pathological vascular structure. On account of the possibility of radiological and clinical masking of renal tumours surgical exposure is recommend if there is the slightest uncertainty. Immunological parameters are not reliable in early and differential diagnosis, since a significant reduction of immunizability does occur in the case of tumours. This phenomenon becomes significant only in patients advanced tumour growth and progressive formation of metastasis.