Abstract Immunization levels of Mexican American and white non-Hispanic infants enrolled in Arizona's Medicaid managed care demonstration project, a prototype of the model proposed for a reformed health care system, were compared and the influence of sociodemographic characteristics, acculturation levels, health beliefs of the mothers, and infant health status on immunization levels were assessed. The study used data collected from office records, birth certificates, and household interviews. The random sample included 292 white non-Hispanic and 274 Mexican American infants. White non-Hispanic infants received more immunizations by age 1 than the Mexican American infants. However, after controlling for a full set of explanatory variables in a multiple regression analysis, ethnicity was no longer a significant predictor of immunization levels. Significant predictors of a higher number of immunizations included fewer siblings, older maternal age, and higher maternal education. Health insurance and enrollment in a managed care plan were not sufficient to ensure adequate immunization of these Medicaid enrolled infants. Results are discussed in terms of previous research and the essential functions of public health as outlined in the Institute of Medicine's Report on the Future of Public Health.