The proteolytic activity of calf rennet on goat casein (CN) was studied under various conditions which affect cheesemaking and ripening processes (pH, salt, calf rennet concentration and α(s1)-CN polymorphism). Electrophoretic studies showed that goat casein was hydrolysed to give characteristic breakdown products derived from individual caseins (β-I to β-V from β-CN, primary hydrolysis product from α(s1)-CN, para-κ-CN from κ-CN and other degradation products from α(s2)-CN). Both goat β-CN and α(s1)-CN were more sensitive to hydrolysis than their bovine counterparts under the same conditions. The pH did not influence the proteolytic specificity of rennet on β-CN, but rennet activity was highly dependent on the pH. However, in the case of α(s1)-CN, the rate of proteolysis and the nature of breakdown products were pH-dependent. NaCl affected only the rate of proteolysis. After prolonged incubation times, the electrophoretic patterns of hydrolysates produced from whole goat casein by rennet were similar to those produced from isolated β-CN, showing that β-CN and its degradation products are quite resistant to proteolysis compared with α(s1)-CN and its primary hydrolysis product. Rennet hydrolysates of goat casein, containing different α(s1)-CN genetic variants, showed slight differences in the electrophoretic profiles which tended to disappear as hydrolysis advanced.