A giant cell induced byRotylenchulus macrodoratus in soybean roots is described from light and electron microscope observations. The cell was usually initiated in the pericycle or endodermis tissues and expanded into the stele. Cell expansion was associated with increased cytoplasmic density and elimination of the central vacuole, cell organelle proliferation, extreme nuclear and nucleolar hypertrophy and nuclear lobing, and uneven wall thickening with irregular lignified wall ingrowths in some sites. In most of these characters, the giant cell is not unlike similar structures formed by heteroderid nematodes, but the uninucleate condition of theR. macrodoratus-induced giant cell is a feature which has not previously been described in host cells associated with plant parasitic nematodes. This giant cell is evidently formed from a single cell.