This study examined the developmental toxicity caused by three butanol isomers. The isomers, which are used as industrial solvents, were 1-butanol (71363), 2-butanol (78922), and t-butanol (75650). Pregnant Sprague-Dawley-rats were divided into three treatment groups of approximately 15 rats each. For 7 hours each day on gestational days one through 19, rats were exposed by inhalation to the isomers. Rats were exposed to 0, 3500, 6000, or 8000 parts per million (ppm) 1-butanol; 0, 3500, 5000, or 7000ppm 2- butanol; or 0, 2000, 3500, or 5000ppm t-butanol. On gestational day 20, the rats were sacrificed and half the fetuses examined for skeletal malformations and the other half examined for visceral malformations. Maternal toxicity was produced by each of the butanol isomers as evidenced by reduced weight gain and food intake. The isomers also produced lower fetal weights which were dose dependent. External fetal malformations were not observed. Most of the skeletal malformations observed were rudimentary cervical ribs which generally increased with increasing concentrations of all three isomers. Occasional visceral variations were seen but were not affected by butanol treatment. The authors conclude that although high concentrations of the three isomers produced developmental toxicity, the isomers are not thought to be strong developmental toxicants and would not produce developmental toxicity in rats at concentrations currently permitted in the workplace.