Phototherapy with either daylight or blue lamps resulted in the development of the bronze baby syndrome in 13 infants. 'Thermotherapy' with an incandescent bulb emitting light mainly in wavelengths not effective for phototherapy caused this syndrome in the 14th infant with respiratory failure. Hepatic dysfunction was present in all infants. The infants were well in spite of the bronzing, after their initial condition had improved. Bronzing disappeared within two months in all but one infant; in eight infants with regular blood examination, the hepatic function became normal by ten months of age, but spectroscopy demonstrated the presence of the pigment(s) even at one year. Normal development was observed.