Increasing numbers of neonates are being admitted to hospital because of extreme jaundice. Phototherapy should be very effective in such infants, because the efficacy of phototherapy is proportional to the concentration of bilirubin in the skin. Here, I report on four infants who were admitted for indirect serum bilirubin levels of >500 micromol/l (>>30 mg/dl). In one of them, unrecognized Rhesus immunization was the main cause of hyperbilirubinemia, while in the other three increased enterohepatic circulation of bilirubin was thought to be an important contributory factor. In all four infants phototherapy (11-14 microW/cm2/nm) with whole body exposure plus ad lib feeding with milk were initiated immediately upon admission to the nursery. After 2h serum bilirubin values were reduced by 170-185 micromol/l (10-11 mg/dl) in the first three infants, while in the fourth infant a reduction of 195 micromol/l (11.3 mg/dl) was seen in the 5 h interval between the first and second bilirubin measurement. This experience suggests that in some infants with extreme jaundice, intensified phototherapy plus feeding with milk may be very effective in reducing serum bilirubin levels. Even if an exchange transfusion is performed, using this strategy in the waiting period may be beneficial, as both the rapid reduction in serum bilirubin levels as well as the conversion of significant amounts of bilirubin into water-soluble isomers may reduce the risk of neurotoxicity.