OBJECTIVE: The use of generic drugs has not been as successful as hoped in France. In order to increase their use, rights of replacement have been given to pharmacists through 1999. The aim of this study is to determine the factors influencing prescription of generics by doctors and generic substitutions by pharmacists. METHODS: We have analyzed reimbursement data from a Department (CPAM93) which has drug-dispensing data from 15 June 2000. The AFSSAPS and the Sempex Data databases were used to evaluate reimbursement data. Chi-square and logistic regression tests were used to establish determining factors for prescribing and replacing with generic drugs. RESULTS: The file analyzed contained 25,422 reimbursement prescription lines involving 6578 patients. Sixty percent of the patients were women, 1964 carried exemption certificates (EXOTM) and 953 received CMU (general state health coverage). The average age of the patients was 43.3 years. The drugs belonging to the AFSSAPS repertoire consisted of 3902 prescription lines. There were 1257 generic drugs that could either be prescribed by the doctor or dispensed in replacement. Three hundred seventy five prescription lines were replaced by pharmacists, or 12.42% of those which could have been replaced. Four products represented more than half of the replaced drugs. The patient characteristics considered by the pharmacist when replacing the drug were lack of EXOTM, age below 65 years old, and the presence of CMU. Prescriptions for generic drugs by the doctor made up 53.50% of the generic prescription lines dispensed, although only 18.20% of the lines reimbursed were on the AFSSAPS listing. CMU, lack of an exemption certificate (EXOTM) and age under 65 years old were the factors taken into account by the doctor when prescribing generic drugs. CONCLUSION: The use of generic drugs in France could be much more widespread.