In the extra-intestinal fluid of Carabus beetles (Carabidae, Coleoptera) the total proteolytic activity was measured against casein. The trypsin and chymotrypsin-like proteases in the extra-intestinal fluid of the beetles were verified by the esterolysis of TAME and BTEE from 1 hr before to 216 hr (ten days) after feeding. Before feeding, both enzyme activities were high and they decreased very sharply after the beginning of feeding. The inhibition characteristics of various naturally occuring trypsin inhibitors were tested: soybean trypsin inhibitor, lima bean trypsin inhibitor, pancreas kallicrein inhibitor and chicken ovomucoid. Affinity adsorption with soybean trypsin inhibitor combined with isoelectric focusing enabled a comparison of the band pattern of serine-proteases in various species. Most of the tryptic and chymotryptic enzymes are acidic with an isoelectric point (IP) between pH 3 and 6. Proteases with an IP of about pH 7 were found only rarely. The interspecific variability of the serine-proteases in higher than the intraspecific one. In addition to the enzymes typical of Carabus lineatus and Carabus splendens the natural hybrids showed new serine proteases.