The influence of actinomycetes, bacteria, and fungi onAphelenchoides parietinus(Bastian, 1865) Steiner, 1932, a fungus-feeding nematode, was studied. Thirty percent of the actinomycete cultures tested showed some "attraction" for this nematode on agar plates. The filtrates from a number of these actinomycete cultures favored accumulation of nematodes on areas of agar on which the fluids were spotted. In some instances the nematodes were repelled from these areas. Of the 60 bacterial isolates from rhizosphere soil only one "attracted" the nematode; most of the others repelled it. The filtrates from most of these bacterial cultures were similarly unfavorable. The nematode aggregated strongly around 43 of 54 cultures of fungi, and propagated on 32 of these. The results suggest that the microflora of the root zone may exert a marked effect on the accumulation of this nematode therein.