In 1991 and 1992, the US Food and Drug Administration approved two acellular pertussis vaccines combined with diphtheria and tetanus toxoids for use as the fourth and fifth doses after the initial three-dose primary series with the standard whole-cell pertussis vaccine administered at 2, 4, and 6 months of age. Recently completed trials of acellular pertussis vaccines conducted in Europe have documented the efficacy of these vaccines when administered as a primary series in infancy. Based on these studies, two acellular pertussis vaccines, Tripedia (Connaught Laboratories, Swiftwater, PA) and ACEL-IMUNE (Wyeth-Lederle Laboratories, Pearl River, NY), were licensed by the Food and Drug Administration for the initial three-dose series. Additional acellular pertussis vaccines are likely to be licensed for use in infants in the future. The recommendations in this statement supplement previous American Academy of Pediatrics guidelines for the use of acellular pertussis vaccines.