After introducing a computer assisted repeat prescribing programme into a south London practice improvements were made in several aspects of practice organisation. Time was saved by doctors and receptionists; prescriptions were produced more rapidly; information in the records about drugs that were available for repeat prescription was improved; and queries from chemists about prescriptions were reduced. The costs of the system in terms of computer operator time were estimated. Computerising prescribing data provides a source of data that may be used to enable doctors to audit their own prescribing.