The addition of [14C]-glucosamine to media of Babesia canis cultures causes the appearance of labeled glycoproteins in the culture supernatants. These radioactive soluble glycoproteins were separated according to their molecular weight by gel filtration and according to their (acidic) pI by preparative electrofocusing. The labeled fractions were then analyzed by SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). The results showed three series of glycoproteic antigens. The molecular weights for the three antigens determined by gel filtration and by SDS-PAGE were approximately 100, 40, and 12.5 kDa, and the preparative gel electrofocusing suggested that the antigens focus in the pH range of 3-5.