The analysis of antigen E of ragweed pollen by polyacrylamide gel electrophoresis in sodium dodecyl sulfate (SDS) resulted in the demonstration of two subunits of molecular weights of about 20 000 and 14 500. These results confirm earlier studies on antigen E by gel chromatography that demonstrated a two-polypeptide subunit composition. Treatment of antigen E with 1% SDS (in the absence of reducing agent) resulted in the dissociation of the two polypeptide chains, which indicates that the bonds bridging the subunits are non-covalent in nature.