Objective: To examine changes in the rate of beta-blocker (BB) use at admission, in hospital, and at discharge between 1994 and 1995 (MICH I) and 1997 (MICH II) in patients with acute myocardial infarction (AMI).Design: Comparison of two prospectively enrolled cohorts.Setting: Five mid-Michigan community hospitals.Patients: We studied 287 MICH I patients and 121 MICH II patients with AMI who had no contraindications to BB use from cohorts of consecutively admitted cases of AMI (814 in MICH I; 500 in MICH II).Results: Prescription of BBs to ideal patients with AMI increased in patients with previous history of myocardial infarction on arrival at the hospital (12.5% vs 36.0%; P= .01), in hospital (47.0% vs 76%; P < .01), and at discharge (34.0% vs 61.9%; P < .01). Neither race nor gender was a predictor of BB use. Younger age predicted BB prescription at discharge (odds ratio [OR], 2.07; 95% confidence interval [CI], 1.32 to 3.23). Later study cohort was the most important predictor of BB use in hospital (OR, 3.4; 95% CI, 2.09 to 5.25).Conclusion: BB use improved dramatically over the study period, but additional work is needed to improve use of BB after discharge and among elderly patients with AMI. [ABSTRACT FROM AUTHOR]