A recently described automated microparticle enzyme immunoassay (Abbott IMx CA 125) for cancer antigen 125 (CA 125) was recalibrated by the manufacturer to provide better agreement between the results of the IMx assay and other test methods for CA 125. The recalibrated microparticle enzyme immunoassay (MEIAII) had low imprecision (2.9-11.9%), a low detection limit (less than 0.48 kU l-1), a low carryover (less than 0.014%), and CA 125 was linearly recovered after dilution. CA 125 was measured during treatment of 138 patients with ovarian cancer and the MEIAII results were closely, but non-linearly, related to antigen values determined by a routinely used manual enzyme immunoassay (EIA) (Abbott CA 125 EIA). EIA levels below 167 kU l-1 resulted in higher values when measured by the MEIAII and CA 125 concentrations above 167 kU l-1 in the EIA gave lower MEIAII values. CA 125 MEIAII and EIA measurements before a second-look laparotomy of 57 patients with ovarian cancer demonstrated that, using slightly different upper limits of normal values (MEIAII, 27 kU l-1; EIA, 20 kU l-1), the clinical information obtained from the MEIAII was equivalent to that obtained from the EIA. In conclusion, switching from the EIA to the MEIAII would indicate that series of samples should be analysed by both methods during a transfer period. The length of the period should depend on the obtained results.