This study was conducted to test an instrument for measuring the level of institutionalization (LoIn) of health promotion programs. Institutionalization occurs when a program becomes an integral part of an organization, and the LoIn instrument is a beginning effort to measure the extent of program integration into organizations. The instrument is based on theory that holds that organizations are composed of production, maintenance, supportive, and managerial subsystems. Institutionalization occurs when a program becomes imbedded into these subsystems. A questionnaire designed to test this construct was mailed to 453 administrators in 141 organizations that operate health promotion programs. Based on 322 usable responses (71%), a confirmatory factor analysis was conducted. The results support the hypothesis of an eight-factor model: four factors concern how routinized the program was in each subsystem and four factors concern the degree of program saturation within each subsystem. Correlations of the eight factors with the number of years the programs had been in operation, and managers' perceptions of program permanency, indicated that the four routinization factors were more highly correlated with program longevity than the four niche saturation factors, and the niche saturation factors were more highly correlated with managers' perceptions of program permanence than the routinization factors. The instrument, which is available from the authors, may be used as both a research instrument and a diagnostic tool in assessing the institutionalization of health promotion programs.