There are few available data on the effectiveness and safety of medical practice guidelines when used for patient care in the coronary and intermediate care units. The aim of this study was to examine the effect of educating physicians about practice guidelines to promote shorter lengths of stay for "low-risk" patients hospitalized with chest pain. Such guidelines were disseminated to physicians working in a health maintenance organization (HMO) by educational conferences, written memoranda, endorsement by opinion leaders, concurrent written feedback, and nursing-to-physician cues. A total of 208 patients were enrolled in the study. Following implementation of the practice guidelines, hospital lengths of stay were reduced from 2.51 +/- 2.1 to 1.96 +/- 1.3 days (22% reduction, p = 0.03) and intermediate care unit lengths of stay from 33.9 +/- 19 to 28.2 +/- 14 hours (17% reduction, p = 0.02) for patients with low-risk chest pain. The reduction in length of stay for patients with low-risk chest pain exceeded reductions in stay for patients hospitalized with cardiac conditions for which no guidelines were introduced. None of the patients treated according to guideline recommendations had unexpected "life-threatening" adverse events in the 2-week period after hospital discharge (95%, confidence interval 0%, 3%). This study supports the effectiveness and possible safety of practice guidelines to reduce lengths of stay for patients with low-risk chest pain.