In 28 patients with non-seminomatous testicle tumour the tumour markers human chorionic gonadotropin (HCG) and alpha-fetoprotein (AFP) were determined radioimmunologically and enzymeimmunologically, respectively. While tumours with chorionic carcinoma (n = 8) always were marker-positive, in the embryonic carcinoma in 2 out of 10 cases falsely negative findings appeared. On 5 patients the biochemical monitoring of the course of the testicle tumour disease is demonstrated in detail by means of HCG and AFP and estimated as very helpful method. Advantages and problems of the marker diagnostics are shown and discussed. The positive marker findings were absolutely evident for a metastasation. On the other hand, marker negativation was not always to be equated with absence of a tumour and demanded a further control of the patient by means of all other available methods of diagnostics up to the second-look-operation.