AbstractA single 1.0‐ml volume of L‐ or D‐carnitine solution, at several selected mmole concentrations, was applied to the extraembryonic membranes of 3‐ and 4‐day chick embryos in ovo. Hamburger‐Hamilton stages of chick development ranged from 17 to 23. During the 17–18th days of incubation, embryos were dissected, and both survival and intracardiac anomaly rates were determined. Only at extremely high doses, both stereoisomers of carnitine exhibited a statistically significant toxigenic effect (p<0.001) as measured by a sharp decrease in survival rate when compared to chick Ringer's saline controls. Furthermore, since the anomaly rates became significant only near the LD50's, this indicated that intracardiac anomalies were induced only at toxic doses. Therefore, it is suggested that cardiovascular teratogenicity may be the result of toxicity. Below the LD50, anomaly rates were not significantly different from those of control embryos. In comparison, L‐ and D‐carnitine were significantly different from one another (p<0.001) both in survival rate and percent affected embryos at a dose of 0.5 mmole. In summary, exogenous carnitine administration to the chick embryo does not appear to be deleterious to the developing card