Enzymes predominantly responsible for the primary degradation of protein in soft cheese and for the related changes in consistency were studied. Reconstructed Noordhollandse Meshanger cheese and preserved simulated soft cheeses of different composition were used as models in the investigation. Results for proteolysis in the simulated cheeses were comparable and also comparable to those observed with normal Meshanger cheese. Protein breakdown was studied by estimating the amount of nitrogen soluble in the moisture of cheese and by quantitative polyacrylamide gel electrophoresis. Results of the two methods were well correlated. Proteolysis, which is primarily responsible for changes in consistency of soft cheeses, was caused mainly by calf rennet enzymes. The activity of rennet at different pH and concentrations of NaCl in the moisture of cheese also revealed a major role of rennet enzymes in protein breakdown in soft cheeses with an initially very low pH, ripening under the influence of a surface flora. The role of the surface flora is merely to regulate pH and so to soften the cheese body, and to give the cheese a specific flavour. Milk protease activity in soft cheese was studied in relation to pH, concentration of NaCl in moisture, ripening time and ripening temperature of the cheese. Its contribution to soft cheese ripening is minor, perhaps except for certain cheeses with a surface flora. Milk protease showed considerable activity in milk at favourable temperatures, proteolysis increased when cheese milk was subjected to low-temperature pasteurization.