OBJECTIVES: Diminishing the cost of a group of highly prescribed drugs in the Comunidad Valenciana (Spain) through the promotion of prescribing them by drug name (not registered names) and the corresponding dispensation at pharmacies of a selected group of registered drugs with the same composition and size and lower price: reference drugs. METHODS: The drugs that represent about 50% of the drug prescription costs for the Health Service in june 1995, were selected through the analysis of the bill paid to the pharmacies. The most prescribed sizes for each drug were studied in order to select those that have minimum prices as reference drugs. An agreement was concluded with pharmacies to dispense these trade names when the prescription was made by drug name. Physicians were informed of it in order to promote prescription by drug name. RESULTS: 34 drugs were responsible of the 45% of the drug prescription bill of the Health Service in the Comunidad Valenciana in june 1995. The first ten of them were: Omeprazole, Nimodipine, Ciprofloxacin, Enalapril, Calcitonin, Diltiazem, Fluoxetine and Nifedipine. Globally, prescriptions by drug name have increased from 0.2% to 0.34% in five months. Prescription of registered names of minimum price has increased markedly for near each drug. i.e.: for Amoxicyllin prescription of reference drugs in 1995 was 14.62% of the total of Amoxicyllin prescription and 35.92% in 1996; for Diclofenac, prescriptions of reference drugs represented 15.02% of the total of Diclofenac prescriptions in 1995 and 31.85% in 1996. CONCLUSIONS: The minimum increase in dispensation of prescription by drug names is influenced by the fact that in Spain there are not generic drugs available and so there is a strong tradition of registered names prescription. The agreement with pharmacies represents the dispensation of a group of selected trade names of minimum prices (reference drugs) and physicians have prefered prescribing directly the names included in this group. The effect of diminishing costs has been obtained with this intervention but not by the increase in prescriptions by drug name as the impact of his measure in prescribing habits has been slight.