Tumour associated monoclonal antibody against placental alkaline phosphatase (H17E2) was radiolabelled with Indium-111 and Iodine-123 and administered intravenously in 33 patients with primary and/or metastatic testicular tumour, as well as in 8 patients who were in complete remission after surgical excision of the tumour. The presence of a tumour was confirmed and correlated well with conventional diagnostic techniques and, in addition, the antibody scan revealed the presence of active disease in 2 patients with negative conventional imaging and with elevated serum markers. In addition, in one patient the CT produced a false positive result where the antibody scan was negative. Finally, the absence of tumour was confirmed in all 8 cases of patients in complete remission. All patients studied with Indium-labelled antibody had observable concentrations of the radiolabel in the liver (estimated to be approximately 30% of the administered dose), as well as in the kidneys and spleen. The patients studied with the Iodine-123 labelled antibody had observable concentrations in the thyroid gland and the stomach. The best images were seen at 48 and 24 hrs after the Indium and Iodine radiolabelled antibody respectively. No human anti-mouse antibody was detected in any of our patients, even in those who received 2 and 3 administrations, with the highest amount of administered protein being 800 micrograms. No toxicity was encountered in any of our patients in 4 months of follow-up. This method may be of clinical value in patients with testicular neoplasma and represents a new addition to current imaging techniques. A positive scan indicates the definite presence of a tumor.(ABSTRACT TRUNCATED AT 250 WORDS)