A program in which pharmacists were authorized to change parenteral histamine H2-receptor antagonist (H2RA) therapy to the oral route without first contacting the prescriber was evaluated on cost and appropriateness of use of the parenteral route. Parenteral therapy was received by 264 and 244 patients in the study and comparison groups, respectively. Length of parenteral H2RA therapy was less in the study group (4.8 vs. 7.5 d) as was length of total (parenteral + oral) therapy (8.4 vs. 12.1 d). Parenteral H2RA drug acquisition savings were $6225 in the six-week study period or $53,950 when annualized. Decreased oral therapy contributed additional savings. There was a significant decrease in the number of inappropriate parenteral doses of ranitidine per patient, the drug used in more than 80 percent of the patients. In addition to the direct effect of pharmacists' interventions, there appeared to be an indirect effect of the program, as physicians initiated route of administration changes on their own.