SUMMARYInfections of Phaseolus with Endogone and Rhizobium compared with Rhizobium alone had increased growth, reproduction, number and weight of nodules, acetylene reduction rates, leghaemoglobin, phosphorus and total protein contents. Shoot/root ratios were lower in the dual infected plants. Levels of infection by Endogone influenced nodulation and the application of soluble phosphate simulated the effects of the fungus. The significance of these additive effects of dual symbiotic infections is discussed.