Proteolysis in Meshanger cheese, estimated by quantitative polyacrylamide gel electrophoresis is discussed. The conversion ofα s1 -casein was proportional to rennet concentration in the cheese. Changes in consistency, after a maximum, were correlated to breakdown ofα s1 -casein. The changes in structure of the cheese during ripening, studied by electron microscopy, looked similar to those reported for Camembert cheese. Softening of cheese with high moisture content was due to rennet breakdown ofα s1 -casein. Tests with substrates of sodium paracaseinate, calcium paracaseinate-calcium phosphate complex and a synthetic complex of casein, calcium hydroxide and phosphoric acid revealed that Na + and Ca 2+ both influenced rennet proteolysis in those systems. Their interaction was considerable and depended on the type of substrate. In cheeses of lower moisture contents than Meshanger cheese, firmness was primarily regulated by volume fraction of protein in the fat-free cheese. Differences in protein breakdown cannot simply be attributed to differences in moisture content.