Trichoderma harzianum and Trichoderma viride were tested for their capacity to reduce the incidence of the root-knot nematode Meloidogyne incognita on tomato. In vitro studies demonstrated that all tested isolates were effective in causing nematode mortality compared with the control. Trichoderma slightly reduced nematode damage to tomato in vivo. Treatment of the soil with the biocontrol agents before transplanting, improved control over treatment directly at transplanting. The Trichoderma isolates could not be re-isolated from the endorhiza, but were successfully re-isolated from the rhizosphere 45 days after fungal inoculation. Only slight increases in plant growth could be measured. The mutualistic endophyte F. oxysporum 162, used as positive control, was more effective in root-knot nematode biocontrol than the Trichoderma isolates.