Interaction of Belonolaimus longicaudatus, Meloidogyne incognita, and Pratylenchus brachyurus on corn and B. longicaudatus, M. incognita, and Heterodera glycines on soybean was investigated in micropiots during two seasons for corn and one season for soybean. Changes in population densities and effects on plant growth of each nematode on corn or soybean alone and in mixed culture were compared. No interactions occurred on corn in 1987. In 1988, midseason population densities of B. longicaudatus were greater in corn plots infested with M. incognita (P = 0.05), but at harvest, population densities or B. longicaudatus were less in corn plots infested with P. brachyurus (P = 0.05). Except for stalk weight at harvest, plant growth was not affected by any treatment. In soybean, midseason densities of M. incognita were increased in combination with H. glycines (P = 0.05), but this trend reversed at harvest. Soybean yield was reduced in plots infested with H. glycines (P = 0.001), whereas B. longicaudatus or M. incognita had no effect on plant growth either singly or in mixed culture. Key words: Belonolaimus longicaudatus, corn, Glycine max, Heterodera glycines, interaction, Meloidogyne incognita, Pratylenchus brachyurus, soybean, Zea mays.