F(ab')2-fragments of the anti-melanoma monoclonal antibody Mel-14 were labelled with123I for external scanning and withl25I for tissue measurement of radioactivity and injected intravenously into patients scheduled for surgical resection of a glioma. The paired-label study was performed by injecting simultaneously131I-labelled control (F(ab')2-fragments. The patients were scanned by computerised tomoscintigraphy. After surgery, the activities of125I andl3I were counted in tumour and normal tissues. The results indicate that there was a low but definite uptake of the antibody in the tumour due to its specificity. The external detection was difficult because of accumulation of antibody fragments in the skull.