In order to develop a technique for screening accessions of Desmodium ovalifolium for resistance to Pterotylenchus cecidogenus, the stem gall nematode, some aspects of the nematode's behaviour were examined. P. cecidogenus moved more readily from dead than from live plants of D. ovalifolium and more nematodes left galls via gall tissue than through healthy stem tissue. An improved extraction technique yielded 650 nematodes per gram fresh weight of gall during 38 hours. Nematodes moved little either vertically or horizontally in soil. In July 1984, most nematodes in an infested field of D. ovalifolium were found in the 40 cm of stem closest to the base but with another clustering of nematodes between 50 and 80 cm. Nematodes moved 40 cm above the plant base between July and September. Plant resistance to P. cecidogenus was unrelated to key aspects of host-finding behaviour including attraction to stems, vertical movement on stem and penetration into seedling roots or shoots.