Overuse of antibiotics is a public health problem and has raised discussions concerning their rational use. This cross-sectional study focuses on the use of systemic antibiotics under the Belo Horizonte Municipal Health Department, Minas Gerais, Brazil, evaluating prescriptions dispensed in March 2002, based on WHO indicators for antibiotic use. On average, 20% of prescriptions dispensed involved at least one systemic antibiotic, among which approximately 46% originated from health care facilities not belonging to the municipal system itself. Amoxicillin was the most frequently prescribed antibiotic, followed by benzathine penicillin. Recording of technical data (dose, intervals between doses, administration, and treatment period) varied from 23.6 to 99.6%. Some 10% of prescriptions failed to specify the treatment period. The study showed the need for rules to allow quality improvement of antibiotic prescriptions, assuring the rational use of such medication by municipal health services.