The work reports the application of the hazard Analysis Critical Control Point (HACCP) procedure to a plant producing "mozzarella" cheese located in Tuscany. The presence of pathogens (Salmonella spp. L. monocytogenes), of indicators of hygienic defects (S. aureus, E. coli), and of microrganisms responsible for the decay of flavour and appearance of the product (Pseudomonas spp.) were detected. The microbiological survey was extended also to confined air of workplaces, to surface of equipment touching the product and to water used for the production of cheese. The results we obtained can be considered satisfactory.