Working with dwarf bean plants, the authors studied changes in the lengths of fungal mycelium in rhizosphere and non-rhizosphere soil at different stages of plant growth, using the soil-agar film technique. In general it appears that the stimulation of microbial growth in the rhizosphere was slight in the early stages of plant growth; the length of mycelium in rhizosphere soil increased with increase in vegetative growth of the plants, and decreased markedly at senescence of the plants.Respirometric studies on rhizosphere and non-rhizosphere soil samples indicated greater activity in rhizosphere soil. The degree of stimulation of activity in rhizosphere soil varied according to the stage of plant growth, with maximum activity corresponding to the stage of maximum vegetative growth of the plants.