Background. Proteolytic enzymes may serve multiple functions: they may inhibit the host′s blood clotting, protect the parasite from the host ′s immune response, facilitate parasite′s migration within a tissue by decomposing the tissue barrier, enhance the hatching and moulting of larvae, and play an important role in their feeding. Learning their identity leads to a better understanding of a host-parasite system. The objective of this study was to check, using biochemical methods, if, in addition to proteases, ES products and extracts of 3rd and 4th larval stages of Anisakis simplex (Rudolphi, 1809) contain other hydrolases. Materials and methods. Stage-3 larvae (L 3 ) of A.simplex were removed from Baltic herring, Clupea harengus membras Linnaeus, 1761 caught in the Baltic Sea. Stage-4 larvae (L 4) were obtained from an L 3 stage culture kept in Eagle ′s medium. The solutions containing ES products were collected and dialysed at 4°C against distilled water for 24 h. Larval extracts were obtained by homogenising the larvae in a physiological saline (0.9 % NaCl) solution in a glass homogeniser. The homogenate was centrifuged for 10 min at 3000 G. The supernatant was used in enzyme activity assays. Enzymatic activity of ES products and homogenates of L 3 and L 4 larvae of A. simplex was determined with the API ZYM test. Results. The excretion-secretion product of L 3 and L 4 larvae of A. simplex revealed activities of 10-and 11 hydrolases, respectively. Activity of esterase, esterase lipase, valine arylamidase, and N-acetyl-β-glucosaminidase in the L 4 larvae extracts was higher than the activity of a corresponding enzyme assayed in the L 3 extracts. Only in the case of acid phosphatase, its activity in L 3 ES products was twice that of the activity found in ES products of L 4 larvae. Enzymes such as trypsin, chymotrypsin, and β-glucosidase were not detected in extracts from L 3 larvae. Conclusion. Activities of most hydrolases in the L 4 extracts were higher than the activities of corresponding enzymes assayed in the L 3 extracts. The high activity of these enzymes found in L 4 larval extracts could be related to a different feeding mechanism of stage-4 larvae.