Tamoxifen (TAM), an antiestrogen, has been approved for use by women at risk for developing hormone-dependent breast cancer. Administration of TAM to pregnant CD-1 mice apparently results in reproductive tract toxicity in female offspring. However, there is little or no data describing potential TAM-induced fetal toxicity to women who may become pregnant while receiving prophylactic TAM treatment. In support of the National Toxicology Program's characterization of reproductive and developmental effects of TAM, the present work describes a capillary electrophoresis (CE)-based analytical technique used for detection of TAM and two major metabolites, N-desmethyltarnoxifen (DMT), and 4-hydroxytamoxifen (4-HT) in CD-1 mouse fetal tissue. TAM-derived material was extracted from CD-1 mouse fetuses 2-12 h following TAM administration (100 mg/kg) to dams on gestation day 16. The presence of TAM, DMT, and 4-HT was confirmed in the solvent extracts by nonaqueous CE. The limit of detection of TAM by UV absorption was approximately 675 amol at a signal-to-noise ratio of 2:1. This work demonstrates both transplacental transport of TAM in CD-1 mice and a sensitive analytical technique for detecting low concentrations of TAM and similar compounds in biological tissues.