The use of models for business management and cost control in public hospitals has led to a need for microbiology laboratories to know the real cost of the different products they offer. For this reason, a catalogue of microbiological products was prepared, and the costs (direct and indirect) for each product were analysed, along with estimated profitability. All tests performed in the microbiology laboratory of the "Virgen de la Concha" Hospital in Zamora over a 2-year period (73192 tests) were studied. The microbiological product catalogue was designed using homogeneity criteria with respect to procedures used, workloads and costs. For each product, the direct personnel costs (estimated from workloads following the method of the College of American Pathologists, 1992 version), the indirect personnel costs, the direct and indirect material costs and the portion of costs corresponding to the remaining laboratory costs (capital and structural costs) were calculated. The average product cost was 16.05 euros. The average cost of a urine culture (considered, for purposes of this study, as a relative value unit) reached 13.59 euros, with a significant difference observed between positive and negative cultures (negative urine culture, 10.72 euros; positive culture, 29.65 euros). Significant heterogeneity exists, both in the costs of different products and especially in the cost per positive test. The application of a detailed methodology of cost analysis facilitates the calculation of the real cost of microbiological products. This information provides a basic tool for establishing clinical management strategies.