Polyclonal antibodies raised against soluble extracts of spores of Acaulospora laevis and Gigaspora margarita only cross-reacted in a dot immunobinding assay (DIBA) with heterologous antigens from spores of some of the VAM fungi tested. Major cross-reactivity was between A. laevis and Gig. margarita. Ammonium sulphate precipitation of protein antigens from extracts of these two fungi, or their treatment with periodate, rendered the activity of antibodies specific, indicating that cross-reactions between the fungal extracts in DIBA is probably due to the presence of non-specific glycoconjugates. Analysis of extracts by an indirect enzyme-linked immunosorbent assay (ELISA) gave more specific reactions, and immunoblotting of PAGE-separated extracts showed that homologous antisera reacted with different protein bands in the two fungi.