A microbiological and biochemical characterization of the Fossa (pit) cheese is reported. The cheeses analysed showed differences for the protocol of production and type of cheese-milk used (bovine or ovine). The total number of mesophilic bacteria and the number of specific microbial groups differed among the cheeses. Lactococci used as starters were found at very low numbers. Non-starter lactic acid bacteria (NSLAB) such as Lactobacillus plantarum, Lb. curvatus and Lb. paracasei subsp. paracasei were found at high numbers (5.8-7.8 log cfu g-1). Cheeses produced from pasteurized or raw milks and using lactococci as starters or not showed similar microbiological and biochemical characteristics. High concentrations of NaCl-in-moisture (ca. 11.5%) and a low value of aw (ca. 0.850) negatively influenced the microbial content and proteolysis. The ratio pH 4.6-soluble N/total N (23.6-39.1%) and the concentration of free amino acids (11.37-41.06 mg g-1) were very high and varied with cheeses. Fossa cheeses which contained the highest number of NSLAB also had the highest concentration of amino acids. The principal amino acids were glutamic acid, valine, leucine and lysine. Urea-PAGE electrophoresis of the pH 4.6 insoluble and soluble fractions differentiated the cheeses. Apart from the variations in the protocol of production, the RP-HPLC of the ethanol-soluble fraction showed a peptide profile which was common to all the cheeses. Especially cheeses which had the highest concentrations of free amino acids and the highest number of NSLAB, also contained the highest aminopeptidase, dipeptidase and iminopeptidase activities. Fossa cheeses also showed a moderate lipolysis which varied among the samples: total free fatty acids ranged from 578 to 1676 mg kg-1. The highest concentrations were found independently of the milk used. The principal fatty acids were butyric, caproic, palmitic and oleic acids. Sensory evaluation of the Fossa cheeses showed differences especially related to the extent of proteolysis.