Field trials were conducted for two consecutive years at the Teaching and Research Farm of the Obafemi Awolowo University in the tropical rainforest zone of Nigeria, to investigate the effects of Meloidogyne incognita, Pratylenchus spp., Paratylenchus spp. and Hoplolaimus spp. on three okra (Abelmoschus esculentus) cultivars planted in 4-m alleys between 3-year-old leguminous trees, Leucaena leucocephala and Gliricidia sepium. A nematode-infested field without L. leucocephala and G. sepium was used as the control field. The leguminous trees were pruned at 3-weekly intervals to prevent shading of okra and the prunings were mulched in the alley field. At the termination of the study, okra cultivars in the non-alley field had higher root-knot nematode galling indices than those in the alley field in both the 2005 and 2006 trials. Fruit yields of okra cultivars were higher in the alley than the non-alley field. In the alley and non-alley fields, okra cv. 47-4 recorded the highest fruit yield in both years of the trial. Soil population densities of four genera of plant-parasitic nematodes increased in both the alley and non-alley fields. However, there was a much greater increase in the non-alley field, suggesting that L. leucocephala and G. sepium planted as alley crops have the potential to suppress nematode populations.