There seems to be some disagreement between various investigators as to whether or not it is possible to differentiate between a complete and a partial obstruction of the bile ducts, using radioactive Rose Bengal and carrying out surface counts (scintillation counters). In contrast to the accepted method of using131I-Rose Bengal, we used125I-Rose Bengal in a test series that included eight babies and two children of pre-school age. In using125I-Rose Bengal we were also able to use relatively small collimators, so that we did not encounter any appreciable technical difficulties even when taking surface counts in very small infants. Following the i.v. injection of 0.5 μCi125I-Rose Bengal scintillation counts were carried out in the region of the heart, liver and intestine (left lower quadrant). The curves obtained showed characteristic differences between non-icteric patients and infants showing clinical signs of an obstructive jaundice. Within the latter group, however, it was not possible to distinguish between cases of extrahepatic biliary atresia and other forms of regurgitative jaundice with intact extrahepatic bile ducts (giant cell hepatitis and inspissated bile syndrom with partial intrahepatic biliary atresia)