A hospital's experience with an automated system for screening drug orders for potential dosage problems is described. DoseChecker was developed by the hospital pharmacy department in collaboration with a local university. Pharmacy, laboratory, and patient demographic data are transferred nightly from the hospital's mainframe system to a database server; DoseChecker uses these data and user-defined rules to (1) identify patients receiving any of 35 targeted medications, (2) evaluate the appropriateness of current dosages, and (3) generate alerts for patients potentially needing dosage adjustments. The alert reports are distributed to satellite pharmacists, who evaluate each patient's condition and make recommendations to physicians as needed. One of the system's primary purposes is to calculate creatinine clearance and verify that dosages are properly adjusted for renal function. Between May and October 1995, the system electronically screened 28,528 drug orders and detected potential dosage problems in 2859 (10%). The system recommended a lower daily dose in 1992 cases (70%) and a higher daily dose in 867 (30%). Pharmacists contacted physicians concerning 1163 (41%) of the 2859 alerts; in 868 cases (75%), the physicians agreed to adjust the dosage. The most common dosage problem identified was failure to adjust dosages on the basis of declining renal function. An automated system provided an efficient method of identifying inappropriate dosages at a large university hospital.