A controlled two-year study of the effectiveness of well-child care by pediatric nurse practitioners (PNPs) of 1,152 children, newborns through age 22 months, was made at the Kaiser-Peranente Medical Centers in San Francisco and Oakland, Calif. In this setting of a large, prepaid, group practice health care plan, the PNPs were found to be entirely competent in maintaining the health of their patients, and were generally accepted by the parents. Effects on utilization of medical care facilities were minimal. Costs of well-child care were reduced.