Pharmacists in the US Public Health Service (PHS) provide direct patient-care support activities at the National Institutes of Health, Food and Drug Administration, and the Indian Health Service (IHS). This is the first of a series of articles describing pharmacists' work in the IHS, where most of the pharmacists in the PHS serve. The IHS operates medical centers, hospitals, and ambulatory health centers. Many innovative pharmacy services have been developed within the IHS since its founding in 1955. IHS pharmacists have long performed clinical and educational duties that many of their private sector colleagues are just now assuming. This paper introduces pharmaceutical services within the IHS and describes several of the important professional innovations that have been developed by IHS pharmacists.