The role of the online prescription support functions of a prescription order entry system was analysed and the results of the prescription audit by pharmacists were examined. In the Kochi Medical School Hospital, an online prescription order system has been developed as part of an integrated hospital information system named IMIS (the Integrated Medical Information System), in which all the physicians enter their prescription orders into online display terminals. The prescription order entry system is provided with prescription support functions, which check the entered prescription data, issue warnings, and offer information about drugs or patients. The prescription order system reduces the incidence of simple prescription mistakes and greatly decreases the cases of inquiries by pharmacists. However, results of the analysis show that such functions as warnings of double order and repeated prescription of a drug do not work as well as expected. The system would thus require some kind of intelligence like that of the auditing pharmacists or that of the physicians with accurate knowledge of clinical pharmacology.