We report the distribution pattern of the target antigen of an IgG1 monoclonal antibody, Ki-OC III raised in BALB/C mice against solubilised ovarian adenocarcinoma, in normal tissue and in a collection of human tumour types. Special reference was made to benign and malignant ovarian tumours. The reactive antigen protein purified to homogeneity for a planned amino acid analysis showed three bands between 37-40 kDa. Immunohistochemical analysis revealed a specificity of 98% and a sensitivity of 77%. The tracer kinetics of the radiolabelled antibody were tested on a human ovarian carcinoma cell line in athymic mice. The results were compared to cell lines derived from breast and stomach carcinomas as well as to a human glioblastoma cell line. The results show the preferential uptake by ovarian cancer cells followed by breast cancer cell lines. In animal models, scintigraphic monitoring and direct measurement of the radio-labelled monoclonal antibody showed a preferential accumulation in tumours, in addition to high level signals in the liver, kidney, spleen and heart which were related to degradation, excretion and high circulation. The Ki-OC III reactive antigen could be a potential candidate for immunomonitoring of ovarian and possibly also of breast cancer, for in vivo tumour imaging as well as for histopathologic examinations.