Monoclonal antibodies specific toPenaeus monodonvitellin subunits were produced from mouse immunized with sodium dodecyl sulfate (SDS) treated ovarian extract prepared from gravid ovaries. After fusion of mouse spleen cells with P3X myeloma, hybridomas were selected by indirect immunoperoxidase ELISA againstP. monodonovarian extract. This was followed by dot-blotting against native and denatured proteins from ovarian extract, female haemolymph, and male haemolymph, then by dot-blotting against each vitellin subunit. Hybridoma clones producing antibodies specific to each of vitellin subunits with a molecular mass of 83, 74, 104 and 58, 104 and 45 kD, antibodies specific to the 215 kD protein, an oocyte-specific protein, and one monoclonal antibody specific to haemocyanin were isolated. All monoclonal antibodies could bind to both native and denatured proteins. Western blot analysis of ovarian extract and female haemolymph from gravid ovary prawns separated by PAGE and SDS-PAGE revealed five vitellin subunits, molecular mass of 104, 83, 74, 58 and 45 kD in ovarian extract, and four vitellogenin related polypeptides, molecular mass of 200, 104, 83 and 74 kD in the female haemolymph. From the immunoreactive relationships among these proteins, it could be assumed that vitellogenin may be released into the haemolymph in two forms, 200 and 74 kD, then the 200 kD polypeptide was either processed into the 104 and 83 kD polypeptides, or directly taken up into the oocyte. In the oocyte, the 104 kD protein would be further cleaved into 58 and 45 kD polypeptides while the 74 kD protein would undergo slight modification or remained unchanged. Western blot analysis of vitellin subunits at various stages of ovarian development revealed that the 200 kD protein appeared in the oocyte during early ovarian development and the 45 and 58 kD proteins appeared during the late development.