Camel calf rennet (CCR) and buffalo calf rennet (BCR) were prepared from dried abomasa to study their physicochemical properties and electrophoretic behaviour and to carry out an immunological characterization of the rennet proteins. CCR was more thermostable than BCR. The milk clotting activity of both rennets increased as pH decreased. The optimum temperatures for CCR and BCR were 50 and 45 °C respectively. CCR was more sensitive to increased CaCl2 in milk than BCR. Addition of NaCl to milk in the range 0–100 g/l resulted in a marked decrease in the clotting activity of both rennets. When the rennets were treated with acetone, the activity of BCR was completely destroyed, but that of CCR was unaffected. The proteolytic activity of CCR was higher than that of BCR and pepsin towards both camel and cows' milk caseins at pH 6·0. SDS-PAGE electrophoretic patterns of CCR and BCR proteins gave two major bands with molecular masses estimated as 52 and 39 kDa for CCR and 50 and 35 kDa for BCR. Immunodiffusion and immunoelectrophoresis using anti-CCR serum demonstrated immunological cross reactivity between CCR and BCR.