A comparison of the protein content and patterns in root extracts from non-mycorrhizal and vesicular-arbuscular mycorrhizal [Glomus mosseae (Nicol. et Gerd.) Gerd. et Trappe] red clover (Trifolium pratense L.) has been made. Soluble protein content was higher in mycorrhizal than in non-mycorrhizal roots. After separation by DEAE-cellulose chromatography and electrophoretic analysis, several additional polypeptides appeared in mycorrhizal extracts. In addition, it seems that one of the additional proteins was a plant-induced superoxide dismutase isozyme.