The objective of this work was to study the characteristics of the gastric aspartic proteinases chymosin and pepsin which are constituents of the kid rennet. The two enzymes were extracted from abomasal tissue of one kid from a local indigenous breed, separated from each other by DEAE-cellulose chromatography and then were purified by gel filtration and anion-exchange chromatography. The molecular weights of the purified kid chymosin and pepsin as determined by gel filtration were 36 kDa and 40 kDa respectively. The isoelectric point of kid chymosin was as multiple forms of 3-6 zones at pH 4.6-5.1, while that of kid pepsin was at pH < or =3.0. Kid pepsin contained 0.37 molecules phosphorous per molecule and was totally inhibited by 5 muM pepstatin A, being more sensitive than kid chymosin. Both enzymes were almost equally as proteolytic as calf chymosin on total casein at pH 5.6. Kid pepsin activity was more pH and temperature dependent than kid chymosin activity. In comparison with the calf chymosin temperature sensitivity, the order of increased sensitivity was: calf chymosin <kid chymosin <kid pepsin.