Conditions required for the combined culture of either Glomus caledonium (Nicol. &Gerd.) Trappe &Gerdemann or Glomus mosseae (Nicol. &Gerd.) Gerdemann &Trappe with suspension-cultured plant cells have been investigated. Sucrose levels (0.05 to 0.5%, w/v) lower than those used for growth of plant cells were optimal for hyphal growth of both G. caledonium and G. mosseae. In vitro hyphal growth from chlamydospores of G. caledonium was stimulated by addition of cells of wheat (Triticum aestivum L. cv. Maris Butler), lucerne (Medicago sativa L. cv. Europ) and potato (Solanum tuberosum L. cv. Maris Piper). The presence of wheat cells similarly stimulated hyphal growth from chlamydospores of G. mosseae. Further tests on the effect of lucerne cells on G. caledonium indicated that a volatile substance was involved in the improvement of hyphal growth.