Maternal calcium homeostasis was studied in pregnant Sprague-Dawley- rats treated with embryotoxic doses of ethylene-glycol-monomethyl- ether (109864) (EGME), and compared with homeostasis in virgin rats. Serum concentrations of total calcium, ionic calcium, parathyroid hormone (PTH), 25-hydroxyvitamin-D3, and 1,25-dihydroxyvitamin-D3 were measured to monitor calcium homeostasis. Gravid uterus weight was reduced slightly by gestation day 21 in rats receiving 50 mg/kg EGME. Significant reductions were noted when the dose level was 100mg/kg. Also at this higher dose level liver weight was significantly reduced. A significant reduction in implants in dams treated with 50mg/kg EGME was noted on day 16 of gestation. No live fetuses were noted in the 100mg/kg dose group on gestation day 21. Fetal body weight and number of live fetuses were significantly reduced at a 50mg/kg dose level. Malformations noted were 95 percent cardiovascular in nature. In the serum variables tested there were no significant changes from control levels on day 16 of gestation. By day 21, there appeared to be a dose dependent effect of EGME treatment on most of these variables including a significant increase in total calcium and ionic calcium while 1,25- dihydroxyvitamin-D3 was significantly decreased in groups treated at the 100mg/kg level. While PTH tended to be lower in EGME treated dams, the decrease was not significant. The authors conclude that, in the absence of maternal toxicity, EGME is strongly embryotoxic. The normal shift in calcium homeostasis seen during pregnancy is absent in the dams exposed to EGME.