An abnormally high level of bilirubin in blood serum in the newborn can cause severe brain damage. In the past, the only available treatment for this hyperbilirubinemia was exchange transfusion, which carried dangers of its own. In recent years, however, an alternate treatment, phototherapy, has also become available. Exposure to light over several days reduces the amount of bilirubin present in blood serum, and present evidence indicates that it is effective in doing so. Two observations led to the development of phototherapy. The first, that bilirubin solutions exposed to sunlight or artificial light lost their color, had been recognized for years. The second, that babies exposed to sunlight did not become as jaundiced as infants with less exposure to the light was noted by a nurse in England. Together, these facts prompted the first cli.nical use of phototherapy in 1958 in England. As the availability of sunlight, particularly in northern climates, is unpredictable, fluorescent lighting was used. Several groups of English, South American, French, and Ital-