Because of recent studies indicating possible embryolethality and teratogenicity of FD&C Red No.2, an ad hoc committee was convened by the Food and Drug Administration to consider these questions. The committee suggested a collaborative study by three laboratories [Food and Drug Administration (FDA), Industrial Bio- Test Laboratories (IBT), and National Center for Toxicological Research (NCTR)] in which Red No. 2 was given at 200 mg/kg body weight, by gavage during dose level via water bottle. Appropriate controls were utilized. FDA used Osborne-Mendel stran rats, IBT used Charles River, and NCTR used both strains. No significant increases in skeletal or visceral abnormalities were seen. No significant increase in resorptions was seen in the Osborne-Mendel strain, but the Charles River stain at IBT showed a significant increase in litters with two or more resorptions after dams had been given 200 mg/kg at 0-19 days of gestation. The NCTR study on the Charles River strain also showed an increase in the same parameter for the same dose level and in addition showed a significant increase in the percentage of resorptions per litter. It was concluded that because of the inherent variation and the absence of an increase in abnormalities or other indications of embryotoxicity, there is reason to doubt that this effect is either biologically significant or reproducible.