AbstractSera of a 30‐year‐old Italian female and a 32‐year‐old Japanese female with prolidase deficiency were analysed by two‐dimensional immunoelectrophoresis, rocket immunoelectrophoresis, and single radial immunodiffusion (SRID). In both patients, amounts of transferrin, albumin and IgM were significantly low, while concentrations ofα1‐acid glycoprotein,α1‐antitrypsin,α1‐antichymotrypsin, ceruloplasmin, IgA and Clq were elevated in comparison with levels of these proteins in sera of healthy Italian and Japanese female adults (as normal controls). The amount of haptoglobin was conspicuously high in the Italian patient but remarkably low in th