Physicians' knowledge of dosage and cost differences between injectable and oral histamine H2-receptor antagonists (HRAs) and attitudes toward pharmacist-initiated route conversion of HRAs were assessed. A questionnaire was mailed to 491 physicians two months before implementation of a hospital program that allowed pharmacists to use preapproved guidelines to directly change the route of HRA administration. A similar questionnaire was sent to 488 physicians after five months of program operation. The response rate was 36.0% and 37.5% for the first and second surveys, respectively. In both surveys, almost half of the respondents gave incorrect answers or did not know whether dosage should be altered when HRA route is changed, and about 60% underestimated the relative cost of injectable HRAs. Among respondents who were aware of the program, 28% preferred direct pharmacist intervention; 15% of respondents who were unaware of the program had the same preference. Physicians generally responded positively to statements regarding the acceptability of the program and thought that the pharmacist's role in route conversion was appropriate. Many physicians were ignorant of differences in dosage and cost between injectable and oral HRAs. They generally supported allowing pharmacists to change the route of HRA administration from injectable to oral.