A staff pharmacist intervention program designed to modify inappropriate dosage intervals for i.v. ranitidine and promote timely conversion to oral therapy is described. Records of patients who were receiving i.v. ranitidine were reviewed for eight weeks to determine whether the dosage interval was appropriate and whether they began receiving oral ranitidine within 24 hours of an order for an oral diet or other oral medications. Pharmacists were then asked to determine the proper i.v. ranitidine dosage interval based on creatinine clearance and the oral dosage that would be appropriate when i.v. therapy was no longer indicated. The information was used to complete an intervention form that was placed in the patient's chart. During the baseline phase the i.v. dosage interval was inappropriate for 49 of 139 patients; 617 i.v. doses costing $4214 were administered to 62 patients for whom oral therapy was indicated; conversion to oral therapy occurred appropriately for 39 of 68 patients (57%). In the intervention phase 138 patients received i.v. ranitidine. Pharmacists made 51 recommendations for adjusting the i.v. dosage interval, and 18 were implemented within 24 hours. All six recommendations to convert immediately to oral therapy were also implemented within 24 hours. A total of 280 inappropriate i.v. doses costing $1912 were given to 30 patients for whom oral therapy was indicated. Conversion to oral therapy occurred appropriately for 53 of 76 patients (70%). A simple program of monitoring and intervention by staff pharmacists when i.v. ranitidine therapy is begun can save money and promote the appropriate use of this drug.