OBJECTIVE: In France, since about thirty years, the level of the consumption of pharmacy strongly increased, which increased the public health insurance expenditure. Policies, who were applied, increased the costs of the patients. The physicians were blamed in those drifts. By knowing that the doctor does not have direct financial profits in the recommendation of the pharmacies, we try to understand if his implication direct or indirect in the increase of the level of consumption of medication is founded. This study examines the factors, which influence the prescription of medication of the physicians. METHODS: For the empirical study we used the national base of the data of the French physicians who were observed during the period from 1981 to 2000.The variables used are the seniority of the physician, the structure and the volume of his professional activity, the effects of the competition and locals' standards. RESULTS: The behaviour of the prescription of the physician depend of his type of convention with the State. At the average, the physicians ,who do not have the convention, prescribe 41 Euro of drugs per act, the physicians, who have the price of consultation fixed by the State, prescribe 36 Euro per act and the physicians, who can fix freely their price, prescribe 30€ per act. The prescription is a regulator of the level of activity (- 3.65 for the physicians without the convention, 0.02 for the rest). We find an effect of complement between the pharmaceutical prescription and the prescription of sick leaves' days. Competition has the influence upon the level of the regulation. CONCLUSIONS: The result of this study makes possible to define the inciting policies on the pharmaceutical regulation to ensure a greater effectiveness of the regulation of an ambulatory medicine.