A polyclonal rabbit anti-human lysozyme (Dako) was applied on histological sections from bivalve mollusc and revealed with a mouse anti-rabbit IgG fluorescein conjugated antibody to localise cellular lysozyme in tissues where its activity had previously detected by enzymatic techniques. Labelling occurred in the cytoplasm of epithelial cells covering the body. This is in agreement with the intracellular distribution of this enzyme. In the Lucinid Lucinella divaricata gills, the cytoplasm of bacteriocytes was also labelled. This suggests that antibacterial activity occurred in these cells. Control sections indicate that fluorescence was a consequence of true primary antibody fixation. However, its specificity should be verified by electrophoretical techniques (Western blot).