INTRODUCTION: Cheese should be produced from ingredients of good quality and processed under hygienic conditions. Further, cheese should be transported, stored and sold in an appropriate manner in order to avoid, among other things, the incorporation of extraneous materials (filth) of biological origin or otherwise, in contravention of the relevant food legislation. The aim of the study was to evaluate the hygienic conditions of "prato", "mussarela", and "mineiro" cheeses sold at the street food markets in the city of S. Paulo, Brazil. MATERIALS AND METHOD: Forty-seven samples of each of the three types of cheese were collected during the period from March, 1993 to February, 1994. The Latin square was used as a statistical model for sampling and random selection of the street markets from which to collect the cheese samples. The samples were analysed for the presence of extraneous matters outside for which purpose the samples were washed and filtered and inside, for which the methodology of enzymathic digestion of the sample with pancreatine, followed by filtering,was used. RESULTS AND CONCLUSION: Of the 141 samples analysed, 75.9% exhibited at least one sort of extraneous matters. For the "prato" and "mussarela" cheeses, the high number of contaminated samples was due mainly to extraneous matters present inside the cheese, whereas in the "mineiro" cheese, besides the internal filth, 100% of the samples had external filth.