Two patients with germ cell testicular cancer were submitted to radioimmunotherapy (RIT) by using the monoclonal antibody 131I-radiolabelled (MoAb) H17E2, raised against placental alkaline phosphatase (PLAP). Both patients had been previously treated with repeated chemotherapy regimens assisted by autologous bone marrow transplant (ABMT), that, in the end were unsuccessful, thus necessitating further experimental treatment. RIT was well tolerated and the targeting of multiple neoplastic lesions was satisfactory. Nevertheless, the clinical results of treatment were minimal owing to the extension of the tumour. The data obtained suggest the possibility of applying this form of treatment in patients with minimal residual disease after previous traditional chemotherapy regimens.