The ability to produce monoclonal antibodies to tumour associated antigens, together with advances in immunocytochemistry, provide the potential for establishing a new functional classification of human tumours. This approach was used to investigate whether the expression of CA125, CA1 and the Thomsen-Friedenreich antigens reflected the biological behaviour of ovarian tumours and, if so, had a potential role in the clinico-pathological assessment of ovarian neoplasms. Expression of these antigens was assessed in benign, borderline and malignant ovarian epithelial tumours and attempts were made to determine if there was any correlation between immunoreactivity and tumour grade, histological subtype, FIGO Stage, tumour ploidy or patient outcome. There was no evidence that expression of these antigens had clinical significance, although it is possible that reactivity with antibody OC125 might identify patients in whom CA125 antigen levels in the sera could be used as a marker to monitor disease progress.