A pharmacy program designed to reduce the inappropriate use of aminoglycoside serum assays is described, and the results of an evaluation of the program are reported. If the clinical status of the patient for whom an assay is ordered does not correspond to the indications for the test, a pharmacist calculates predicted aminoglycoside serum levels based on renal function and discourages the physician from having the test performed. If the indications for a test are met, the pharmacist checks for potential interactions. He specifies the exact times serum samples are to be collected, and he prepares a pharmacokinetic report for the physician based on the test results. During the 18-month evaluation, 67 tests were ordered for 53 patients. Three tests were not performed based on pharmacist advice. Five tests could not be evaluated. Of the remaining 59 tests, 56 (95% were used appropriately; 54 of the appropriate decisions made (92%) were a result of the physician following the recommendations of the pharmacist. The program appears to prevent problems that occur when aminoglycoside serum assays are not restricted.