In 24 patients with malignant melanoma the clinical feasibility of immunoscintigraphy (ISC) with a Tc99m-labeled F(ab)2 fragment of an anti-melanoma monoclonal antibody was evaluated. This antibody (225.28S) recognizes a human high molecular weight melanoma associated antigen with restricted tissue distribution, which is expressed on melanoma cells in about 90%. The results of ISC were related with the clinical stage of the patients and the level of invasion of the primary tumor (Clark level). Results of ISC indicate the possibility that patients with the highest Clark level have a higher incidence of false negative scintigrams than those with lower levels of invasion of the primary tumor. In 3 out of 5 patients with Clark level 5 false negative scintigrams were found, whereas in 14 patients with lower Clark levels ISC was true positive, however, the number of metastases was underestimated. 14 of 18 patients with clinical stage II-IIIb had positive scans visualizing 27 of 59 metastases. Thus overall sensitivity was 77% and regional sensitivity 46%. Scintigraphically lesions in lymph-nodes, liver and skin were frequently detected, whereas ISC was less sensitive for lung, bone and brain metastases. No false positive findings were observed by ISC (specificity 100%). Relating the sensitivity and specificity of ISC to the prevalance of disease post-test likelihoods for a normal and an abnormal test result were calculated. Post-test likelihood for the disease with an abnormal scintigraphic finding is 100%. However, with a disease prevalance of 75%, according to our patients, the predicitive value of a normal test result is 60%, thus the post-test likelihood for the disease remains rather high (40%).(ABSTRACT TRUNCATED AT 250 WORDS)