The monoclonal antibody DLE7 was obtained against 44- to 50-kDa polypeptides solubilized from the vitelline envelope of the Mediterranean sea bass Dicentrarchus labrax. In Western blot analysis of chorion lysates it recognized cross-reactive bands at 44 kDa, 48 kDa, and 110 kDa. Previous affinity blotting with concanavalin-A showed that most of solubilized bands were glycosylated. Enzymatic deglycosylation of chorion proteins followed by Western blot analysis with DLE7 showed that the 48-kDa and 110-kDa antigens were differentially affected by endoglycosidase-F treatment. When DLE7 was employed in immunofluorescence analysis, isolated chorions and ovarian cryosections stained intensely. Positivity was also observed in liver cryosections of spawning females but not in liver of males and nonspawning females. To study the origin and delivery of chorion proteins, DLE7 was used in Western blot analysis of liver homogenates and blood serum of spawning females. Cross-reacting bands were detected in liver (90 kDa) and serum (180 kDa, 50 kDa). DLE7 was also used for the first time to set up an indirect ELISA assay to detect egg antigens in the blood of egg-producing females, raising the possibility of using DLE7 as a female-specific marker of spawning for sea bass.