Laboratory methods were adapted or developed to analyze approximately 70,000 daily urine samples collected during more than 2,500 menstrual cycles from 448 women working in the semiconductor industry. An immunoenzymometric assay (IEMA) for human chorionic gonadotropin (hCG) was employed for screening cycles in order to optimize laboratory resources and to reduce the number of samples requiring analysis by less efficient methods. The presence of hCG in urine was confirmed by the definitive immunoradiometric assay (IRMA). The screening assay eliminated 78% of cycles from further analysis because there was no evidence of conception. Thirty-eight of 448 cycles identified as having significant levels of hCG with the IEMA were confirmed as hCG positive with the IRMA. HCG-positive cycles were further evaluated by examination of daily diary data and by laboratory assays for ovarian and pituitary hormones. As a result of these evaluations, 17 of the 38 cycles identified by the IRMA as positive for hCG were found to be nonconceptive cycles. These results demonstrate the effectiveness of screening assays for hCG, as well as the importance of using multiple urinary biomarkers for the detection of early fetal loss with daily urine samples.