Health care researchers rarely employ Medicaid claim files as a data base, in part because they are designed to serve fiscal and administrative ends. Indeed, some investigators have emphasized the deficiencies in such records. In contrast, we have found Tennessee Medicaid data to be suitable for research. A statewide automated data processing system reduces the occurrence of many of the errors noted by others. Further, analysis of the July 1974 month of payment file illustrates the accuracy and internal consistency of Tennessee Medicaid data. Specimen legend drug results for ambulatory patients suggest investigations of physician prescribing patterns. Evaluation of the Medicaid claims processing system suggests other applications in health care administration and research. In a time when available resources are dwindling, the incisive use of Medicaid claims files offers an attractive alternative to expensive new systems of data collection and analysis.