Timed-pregnant New Zealand white rabbits (15 per group) were exposed to methyl tertiary butyl ether (MTBE, CAS No. 1634-04-4) vapor for six hours/day on gestational days (gd) 6 through 18 at target concentrations of 0, 1000, 4000, or 8000 ppm (mean analytical concentrations of 1021=40, 4058-41 and 8021-161 ppm for the 1000, 4000 and 8000 ppm groups, respectively). Maternal clinical signs were taken daily, and body weights were measured on gd 0, 6, 9, 12, 15, 18 and 29. Maternal food consumption was measured daily throughout gestation, gd 0-29. At scheduled sacrifice on gd 29, maternal body weight, gravid uterine weight and liver weight were taken, with upper and lower respiratory tract (including nasal turbinates) retained in fixative. Ovarian corpora lutea of pregnancy were counted and all uterine implantation sites were identified and recorded: resorptions (early or late), dead fetuses and live fetuses. All live fetuses were examined for external malformations (including cleft palate), and variations, for visceral malformations and variations (including craniofacial alterations) and for skeletal malformations and variations.