Tumour associated monoclonal antibodies (MAbs) HMFG1, HMFG2 and H17E2, labelled with 123iodine or 111indium, were used to detect primary and metastatic cancer by external body scintigraphy in patients with ovarian, breast and non-small cell lung cancer (NSCC). Successful localisation was seen in all patients with primary and 80% of the metastatic NSCC, 50% of primary and 70% of metastatic breast cancer lesions and in 80% of patients with metastatic ovarian cancer. On the other hand, imaging carried with a radiolabelled non-specific MAb produced positive results in 3 out of 5 cases with primary NSCC. Therefore, non-specific imaging should be further studied in clinical research for the evaluation of the specificity of radioimmunodetection. A therapeutic procedure which has shown promise is that of intracavity administration of radiolabelled antibodies. Twenty-nine patients with resistant ovarian cancer have been treated with intraperitoneal 131I-labelled MAbs (HMFG1, HMFG2, AUA1, H17E2). There were no significant responses in 8 patients with gross disease. There were 2 responses in 15 assessable patients with tumour nodules of less than 2 cm in diameter. Out of 6 patients with microscopic disease, 4 are disease-free with follow-up time of 6-40 months (mean = 17.5 months).