To assess the role of color Doppler echocardiography in the early postoperative evaluation of patients with a Blalock-Taussig shunt we examined 13 consecutive infants who underwent insertion of either a modified right (6 patients) or a modified left (7 patients) Blalock-Taussig shunt (age range 7 days to 6 months, mean age 8 weeks). Examination of the patients in a high parasternal right or left long axis was able to determine patency of the shunt in 12 patients. In the remaining patient, who did not show flow in the shunt, complete occlusion of the shunt was confirmed by angiography. From subcostal views we were able to demonstrate patency of the shunt in 75% of the infants and in all patients younger than 4 weeks of age. In our experience color Doppler echocardiography is a highly reliable method for early postoperative evaluation of infants with a Blalock-Taussig shunt.