The U.S. Preventive Services Task Force's "Guide to Clinical Preventive Services" summarizes the results of a critical review of the literature pertaining to the effectiveness of 169 interventions in modifying 60 risk factors or conditions. The ultimate impact of the guide depends on the diffusion into clinical practice of its recommendations. This report reviews the factors influencing the diffusion process. Three categories of behavioral influence--predisposing, enabling, and reinforcing factors--apply to this diffusion process. Predisposing factors include knowledge and attitudes, personal health behaviors, confidence, and beliefs about patients' interests in health-promotion advice. Enabling factors include competence to perform preventive services, reimbursement for preventive services, organization of the practice setting, time to provide preventive services, a reminder system, and a coherent set of guidelines that are perceived as scientific and unambiguous. Reinforcing factors include peer support, feedback, evidence of results, and an enhanced sense of self-efficacy in fulfilling one's role as a healer. Recommendations are given for using these factors to increase the diffusion of preventive services into clinical practice.