In 1990 Congress mandated that all state Medicaid programs implement both retrospective and prospective drug-use review (DUR). Nearly a decade later, implementation of prospective DUR (ProDUR) remains incomplete, and few of the implemented systems have been rigorously evaluated. This study was undertaken to analyze the impact of ProDUR screening of beta-agonist inhaler use in the Maryland Medicaid program from 1994 through 1996. The study used a pre/postcomparison series cohort design with data from Maryland, Georgia, and Iowa. Regression analysis was used to control for population differences between states in the year before the ProDUR intervention. The analysis used Medicaid and Medicare enrollment and claims data to select the study cohorts, assess exposure to the ProDUR intervention, develop patient risk profiles, and tabulate rates of adverse clinical outcomes for each subject. The study compared incidence rates for adverse outcomes for 2 1/2 years after implementation of the beta-agonist screens in Maryland, Georgia, and Iowa. Descriptive time plots and regression models were used to test the hypothesis that ProDUR screening reduces the incidence of adverse effects associated with misuse of beta-agonist inhalers. The study end points included 10 clinical outcomes related to therapeutic duplication and drug-drug interactions involving beta-agonist inhaler use by elderly individuals with chronic lung disease. No significant changes in the incidence of these outcomes could be linked to ProDur screening.