A comparative evaluation of the efficacy of fiberoptic phototherapy using the Ohmeda Billiblanket fiberoptic device, conventional phototherapy using daylight fluorescent lamps, and a combination of the two forms of phototherapy was made in 165 term healthy infants and 105 preterm infants with hyperbilirubinemia. In the term infants, the 24-hour decline rate for fiberoptic phototherapy was 9.2% +/- 1.6% (mean +/- SEM) versus 21.5% +/- 1.8% for daylight phototherapy (p < 0.01), and the overall decline rate was 0.49% +/- 0.03%/hr versus 0.70% +/- 0.04%/hr (p < 0.001). Combination phototherapy, with a 24-hour decline rate of 29.9% +/- 1.0% and an overall decline rate of 0.97% %/- 0.04%/hr, was significantly better than daylight phototherapy in both respects (p < 0.01 and < 0.01, respectively). The duration of exposure for fiberoptic phototherapy was significantly longer than that for daylight phototherapy, which in turn was significantly longer than that for combination phototherapy. Response to exposure in the preterm infants was significantly better than that in the term infants with the respective types of phototherapy. The nursing personnel unanimously felt more comfortable with fiberoptic phototherapy, which did not disturb the swaddled infants as much as conventional phototherapy. The parents also felt more reassured. Fiberoptic phototherapy proved adequate in controlling hyperbilirubinemia in preterm infants; in term infants, failures often occurred. Combination phototherapy can be recommended for severe or rapidly increasing jaundice in preterm infants, but its efficacy in term infants is uncertain.