To promote use of essential clinical preventive services, the New York City Department of Health and Mental Hygiene developed the Public Health Detailing Program, a primary care provider outreach initiative modeled on pharmaceutical detailing. Department representatives conducted topical campaigns, making unscheduled visits to health care practices and meeting with providers and office staff members. Representatives distributed "action kits" containing practice tools, provider information, and patient education materials; nicotine replacement therapy was distributed during the smoking cessation campaign. More than 2,500 interactions with practice staff members were completed by six health department representatives at approximately 200 sites. Physician visits lasted 10 minutes or longer, and by provider self-report, use of office systems for prevention and adherence to recommended practices increased. Public health detailing is an effective method of reaching providers to deliver key prevention messages, feasible for public health agencies and acceptable to practices. The effectiveness of this intervention in improving clinical prevention services requires further evaluation.