Increased expenditures for pharmaceuticals in previous years lead to implementation of several cost-containment measures in 2003 in the Slovak Republic. Within that, co-payments for antibiotic drugs were increased from 0 to 1.25€ per package in 2002 and in the beginning of 2003 from 0 to 5€ per package after November, 2003. The consumption of antibiotics significantly decreased from November 2003 compared to the same period the previous year. OBJECTIVES: To assess the influence of increased co-payment of antibiotic agents to their decreased consumption in a retrospective study. METHODS: Consumption of antibiotic agents (group J01 according to ATC classification) prescribed in outpatient care in the Slovak Republic during the period of November, 2003 to April, 2004 was compared to consumption during November, 2002 to April, 2003. Antibiotics were divided into three groups according to the level of co-payment: without increased co-payment, with slightly increased and significantly increased co-payment. RESULTS: Overall consumption in period 2003-2004 decreased by 25.1% compared to the previous year. Consumption was 46.5% lower in the group with the highest increase of co-payment, but only 30.9% or 13.8% lower in the group with slightly increased co-payment and in the group without change in co-payment, respectively. CONCLUSIONS: Increase in co-payment in November, 2003 had a huge effect on the use of antibiotic agents in the Slovak Republic. Although 55% of antibiotic agents had no change in the level of co-payment, the consumption decreased in this group by 13.8%, probably because of awareness of increased co-payments within this group of pharmaceuticals.