An part of a study on possible harmful effects of working in the semiconductor industry during pregnancy, laboratory methods were developed to analyze 70,119 daily urine specimens collected during more than 2,552 menstrual cycles from 448 women employees. Of the 2,036 cycles screened for human chorionic gonadotropin (hCG) using the immunoenzymometric assay (IEMA), 448 cycles met the criteria for a positive screening window. They were subsequently evaluated with the immunoradiometric assay (IRMA). From the set of 1,588 cycles that were negative for hCG in the IEMA, the first 481 cycles with positive pregnanediol-3-glucuronide (PdG) were also tested with the IRMA. All these cycles were confirmed to be negative for hCG. Of the 448 IEMA positive cycles, only 38 were classified as positive for hCG following analysis with duplicate IRMAs. Following additional evaluation of the PdG, estrogen conjugates, luteinizing hormone alpha subunit, and diary data, 17 of these cycles were determined not to be early fetal loss. The authors conclude that daily urine samples can indeed be collected from large population of working women, and can be used to measure biomarkers of reproductive function. Compliance of the workers was excellent. A computerized database management system was used to facilitate accurate logging and tracking of samples, reliable integration of information from different study components, and producing written and graphic reports for monitoring study progress and carrying outdate analyses.