Abstract: Rabbit antiserum raised against isolated human ova produced an intense immunofluorescence and a precipitate on the outer surface of human and porcine zonae pellucidae.The antiserum reacted with none of 22 human tissues nor with any of 4 body fluid components by immunofluorescence or immunodiffusion analysis, but the antiserum agglutinated AB erythrocytes after absorption with O erythrocytes.The anti-zona activity was achieved by higher titres for human than for porcine zonae.Immunofluorescence on porcine zonae was completely abolished by absorption with porcine ova, whereas a weak but definite fluorescence remained on human zonae.These findings indicate that the human zona pellucida consists of at least three distinct components; (1) a specific antigen(s) shared by human and porcine zonae, (2) an antigen(s) specific to human zonae, and (3) a non-specific antigen(s) associated with the blood group substances.