The Indian Health Service (IHS), an agency of the US Public Health Service, instituted a broad range of clinical pharmacy services for ambulatory patients in the 1960s and early 1970s. One outgrowth of these services was that pharmacists were authorized to provide certain prescription legend drugs directly to patients without physician preauthorization. Also, pharmacists monitored patients' progress and were authorized to make therapeutic substitutions of drugs. Pharmacist prescribing privileges in these programs were defined by P & T Committee-approved protocols. Success with these programs led to expanding the pharmacist's role to include physical assessment and differential diagnosis of patients with specific diseases and to manage their care when that care consisted primarily of medications. The development and implementation of these programs and the results of a study of pharmacist prescribing within the IHS are described in this article, as is the IHS clinical pharmacy training program.