The culturing of A. macrogynus and A. arbuscula was re-investigated with particular reference to the selective development of either zoosporangia or resistant sporangia in diploid cultures. The latter required an excess of glucose and a balance of concentrations of methionine and thiamine together with it reduced availability of oxygen. Results suggest that regulatory controls may be exerted by variations in the enzymes and coenzymes involved in the metabolism of pyruvate.