A center-based program was designed and implemented to promote aerobic physical activity among healthy Black-American families with children in the fifth through seventh grades. Ninety-four Black-American families were actively recruited and randomly assigned to an experimental or control group. Families in the experimental group were encouraged to participate in a program with the following features: one education and two fitness sessions per week for 14 weeks; educational sessions that included individual counseling, small group education, aerobic activity, and snack components; located in a convenient building cherished by the community; aerobic activity sessions in a fitness center outfitted and staffed according to modern characteristics; a variety of incentives including free transportation and babysitting and reminders to promote attendance. Percent participation was low, with about 20% participating in the desired fitness center sessions by the end of the program. As a result of low participation, no differences were detected between experimental and control groups on indicators of cardiovascular fitness. In postprogram interviews, conflicts with work and school events were the most commonly reported reasons for nonattendance. We concluded that because of difficulties in attendance, center-based programs appear to have limited value as the sole modality for intervention in public health programs for promoting physical activity among healthy, low income Black-American families with young children. More comprehensive community-based programs are likely to be needed.