To provide an objective rapid means of excluding extrahepatic biliary atresia (atresia), a hepatic index was devised from the ratio of the net hepatic to cardiac distribution of 99mTc diisopropyl iminodiacetic acid or methylbrom iminodiacetic acid between 2.5 and 10 minutes after injection. The hepatic index was compared with subjective assessment of abdominal scintigraphy performed repeatedly over 24 hours. In 22 infants with hepatitis the hepatic index ranged from 5.03 to 14.9, one having no excretion on scintiscan. In 26 infants with atresia the index ranged from 0.49 to 4.26 and in two with paucity of intralobular bile ducts it was 1.85 and 3.69. None of these infants had excretion apparent on scintiscans. Similarly, low hepatic indices occurred in four infants with liver dysfunction but pigmented stools, three of whom had no excretion apparent on scintiscans. These preliminary studies suggest that a hepatic index of greater than 5 is much more rapid and as specific in excluding atresia as repeated abdominal scintigraphy.