A first trial to recognize gelatinous zooplankton using an immunochemical method was carried out. Polyclonal antibodies (rabbit IgG) raised against three cnidarians and four pelagic tunicates were purified and tested for their specificity against various sympatric zooplankton and micronekton. While antibodies to cnidarians were species-specific or at least distinguishable by means of the patterns of the bands appearing, antibodies to the pelagic tunicates cross-reacted with the antigen from the other tunicate species although these did not cross-react with other animal taxa. These results suggest that the present cnidarian antibodies can be applied to the predator identification at the species level. Antibodies to pelagic tunicates would also be effective tools for basic scanning at higher taxonomic levels, i.e. pelagic tunicates or other animals. The antibodies were applied to the identification of the ‘barrel’ of Phronima, indicating that the ‘barrels’ originated from tunicates but not from cnidarians. The present study indicates that the immunochemical method using polyclonal antibodies is a powerful tool for the detection of gelatinous zooplankton.