Such efforts have three major objectives: to teach adolescents to identify early signs of substance abuse, to teach them to assist their peers to recognize and accept the need for treatment, and to provide information on referral resources for friends in need of treatment. Early signs of alcohol and marijuana use are provided, and suggestions for meeting the second and third objectives are offered with emphasis on working closely with existing community treatment and self-help programs. Guidelines are provided for organizing, implementing, and evaluating secondary prevention programs within an ecological framework. Emphasis is placed on the need for honesty and evenhanded presentation of scientific facts. Multidimensional, tenured, and integrated programming is recommended, and examples of school- and community-based programs are described. Resistances to secondary prevention programs are identified, including widespread misunderstanding and failure to appreciate the value distinguishing substance use from abuse, parental fear and denial, and reluctance among school administrators to confront the problem directly. Primary prevention strategies and their combination with secondary strategies also are discussed. 87 references.