Prior studies have evaluated the teratogenicity of TCE, a contaminant of drinking water. However, none specifically examined effects of TCE on cardiogenesis. The purpose of this study was to determine if TCE is a cardiac teratogen in early embryogenesis in an avian model. Fertile White Leghorn chicken eggs were incubated under standard conditions. At stage 6, 12, 18, or 23, TCE, in concentrations of 5 to 25 microM (2 to 28 micrograms/g body weight) was injected into the air space of the egg (vol = 0.03 ml). Mineral oil and saline served as control solutions. For this double-blinded study, solutions were coded and remained so until all observations were made and recorded. Embryonic hearts (n = 1055) were examined at stage 29, 34, or 44. Gross examination was performed, followed by microdissection. Cardiac malformations were found in 7.3% of TCE-treated hearts, compared to 2.3% of saline controls (p less than 0.01), and 1.5% of mineral oil controls (p less than 0.001). No significant difference in incidence of malformations was found when comparing saline and mineral oil controls. Cardiac defects include septal defects, cor biloculare, conotruncal abnormalities, atrioventricular canal defects, and abnormal cardiac muscle. These data demonstrate that TCE is a cardiac teratogen in an avian model.