The ELSA-CA 125 II is a second-generation radioimmunoassay for the quantification of CA 125 in serum. In a multicentre study involving 49 follow-ups of patients with ovarian cancers, and 880 other patients, 2.8% of healthy persons, 25% of 149 patients with benign gynaecological diseases and 39% of 82 patients with benign non-gynaecological diseases had CA 125 levels above 35 U/ml. Using the 35 U/ml cut-off, sensitivities among epithelial ovarian cancers were found to be 85% in serous tumors, 41% in mucinous tumors and 83% in other types. During follow-up of patients with serous ovarian cancers, we observed an equivalent behaviour of both assays--first- and second-generation--with the clinical evolution. We also compared results obtained with other assays commercially available; these were significantly different when a polyclonal antibody was used in the sandwich assay.