Mothers who resided in Brownsville, Texas and who had children with neural tube defects (NTD) were studied to determine whether exposure to environmental mutagens may be a cause of abnormal reproductive outcomes. Peripheral blood lymphocytes from 19 of the mothers who had children with NTD and from 14 matched mothers who had normal children and who resided in Corpus Christi, Texas were investigated using the standard cytogenetic assay and a challenge assay to determine the existence of chromosome aberrations and abnormal DNA repair response. No differences were observed when the spontaneous and the challenged chromosome aberration frequencies were compared between the core and the control groups. Our data suggests that the core group was not exposed to mutagens at levels to cause significant increases of chromosome aberrations or to cause abnormal DNA repair response as determined by our assays. However, exposure to non-mutagenic environmental teratogens cannot be ruled out.