A greenhouse pot experiment was conducted to determine the effect of time of introduction of Trichoderma harzianum on its biocontrol efficacy against Meloidogyne javanica in tomatoes. The experiment consisted of all possible combinations of individual, concomitant and sequential inoculations of T. harzianum and M. javanica. Results indicated that time of the fungus introduction into the soil proved to be important. Introduction of T. harzianum to M. javanica-infested soil at or prior (one or two weeks) to nematode inoculation suppressed the nematode reproduction and increased host growth. However, such effects were increasingly greater when the fungus was introduced two or one week prior to nematode inoculation.