The rate of autolysis after thawing in intact frozen krill (whole body, cephalothorax, and abdomen) and in its homogenates was studied by determining both the increase of TCA-soluble nitrogen and the change of protein pattern in SDS-polyacrylamide gel electrophoresis.Autolysis in the intact state proceeded rapidly in the separated cephalothorax, but very slowly in separated abdomen. The pH dependence in autolysis differed between cephalothorax and abdomen homogenates, indicating differences in the proteolytic enzymes involved. Autolysis of intact whole body proceeded to an extent similar to that of intact cephalothorax, liberating about 30% of total nitrogen in 24 hr. The rapid autolysis of abdomen proteins in the intact whole body was attributed to the action of cephalothorax proteases which penetrate into abdomen.Among muscle proteins, the myosin heavy chain (MW=206,000) was degraded very rapidly and extensively during autolysis.