Proteins of Toxoplasma gondii were separated by SDS-polyacrylamide gel electrophoresis with subsequent transfer to a nitrocellulose sheet by electrophoretic blotting. Immunologically reactive polypeptides were detected by human sera with previously known toxoplasma antibody levels. Heavy chain-specific, peroxidase-conjugated anti-human immunoglobulins were used as the indicator antibodies for the separate identification of IgG and IgM reactive polypeptides. IgG toxoplasma antibodies reacted with several antigens of M r ≈27 000–67 000, while toxoplasma-specific IgM seemed to detect only a few polypeptides. The M r of 35 000 for the dominating IgM reactive polypeptide was observed.
