Three aspects of the production and applications of monoclonal antibodies (mabs) were investigated. Two new cell lines (C23/11 and HET-37) were produced for use as potential fusion partners in human mab production. C23/11 was established from a blood sample obtained from a patient with myeloma. It was shown to have many of the cellular and antigenic properties associated with a lymphoblastoid cell line. HET-37 is a human/murine heteromyeloma cell line which was established after C23/11 cells were fused with murine NSO cells. Both C23/11 and HET-37 were characterised using electronmicroscopy, histology, immunophenotyping, isoenzyme analysis and DNA fingerprinting. In the second experimental section, three mab (HMFG-1, AUA-1 and H17E2) were labelled with the radioactive isotope, Indium-III. They were used for localisation of tumour in 21 patients with suspected ovarian carcinoma. IDIn-mab immunoscintigraphy was found to be a more sensitive technique for evaluation ovarian cancer than X-ray, CAT scan and ultrasound. Inln-mab immunoscintigraphy was particularly useful in localising tumours in patients with serum CA-125 levels greater than 100 IU/ml. F(ab’)2 fragments of HMFG-1 were labelled with technetium and were used to determine the distribution of ovarian tumour in a patient with minimal residual disease. In the final experimental section, HMFG-1 was chemically conjugated to the photosensitiser hematoporphyrin, Hp. HMFG-l-Hp was shown to kill antigen-bearing MCF-7 cells in vitro after irradiation. The HMFG-l-Hp conjugate had no effect on EJ- 138 cells under identical conditions. The EJ-138 cell line does not express the antigen to which the HMFG-1 antibody binds.