The technique of color flow mapping was used to diagnose 19 cases of fetal structural heart disease from a study group of 104 fetuses. Color flow mapping was 76% effective in detecting the presence of fetal structural heart disease. The colored views of a single stream in the atrioventricular canal were most impressive in cases of complete atrioventricular canal, hypoplastic left heart syndrome, mitral atresia, and tricuspid atresia. The colored views of tricuspid regurgitation were also clear in cases of endocardial fibroelastosis, pulmonary atresia with intact ventricular septum, and Ebstein's anomaly. The use of this technique resulted in the in-utero diagnoses coinciding more closely with the final diagnoses, which were made after birth. This was particularly important in those cases which required immediate management after birth.