Groups of 30 mated female rats were given daily doses of 0, 200, 500 or 1000 mg carmine/kg body weight by oral intubation throughout pregnancy. A group of 17 similar animals was given a solution of chlorides to provide an intake of sodium, potassium and ammonium equal to that resulting from the highest dose level of carmine. There were no effects of carmine treatment on body weights, pregnancy rates, pre-implantation losses, the average numbers of live young, litter weights or foetal weights. The group given the highest dose of carmine and the cation control had increased numbers of implantations and post-implantation losses. The latter was considered to be due to an inability to maintain the increased numbers of implantations rather than to an embryotoxic effect. The foetuses showed no malformations and those from the carmine-treated rats tended to have a slightly more advanced degree of ossification of certain skeletal elements than foetuses of the control animals. On the basis of the results obtained it is considered that there were no untoward effects on embryo development in rats given oral doses of up to 1000 mg carmine/kg body weight/day throughout pregnancy.