Eighteen species in eight genera of plant-parasitic nematodes were identified from soil samples collected from soybean fields throughout Missouri. The genera represented were Helicotylenchus, Heterodera, Hoplolaimus, Meloidogyne, Paratylenchus, Pratylenchus, Tylenchorhynchus, and Xiphinema. Three fields, each with high densities of Helicotylenchus pseudorobustus, Pratylenchus hexincisus, or Paratylenchus projectus, were planted in 1989 with six soybean cultivars, with plots of each cultivar either not treated or treated with 5.43 kg/ha aldicarb, to determine whether economically important relationships existed. In none of the sites were nematode densities affected by either aldicarb treatment or cultivar, nor were seed yields related to nematode densities; however, mean seed yield was significantly lower in the P. projectus site. In 1990, seed yield was negatively correlated (r = -0.34, P < 0.05) with P. projectus density at planting. Based on the present and previous studies, H. pseudorobustus and P. hexincisus do not appear to be of economic interest on soybean, but P. projectus probably deserves more study.