Receptivity tests to fusarium wilt of five soils samples in the North of Morocco showed that four of them were suppressive but only one was conducive.The heat treatment destroys almost totaly suppressiveness of these soils, which is therefore microbiological nature. The microbiological analysis showed that the proportion of F. oxysporum in the whole fungal population and the proportion of fluorescents Pseudomonas spp. in the whole bacterial population are higher in resistant soils than in the conducive one. Some strains of nonpathogenic Fusarium oxysporum and fluorescents Pseudomonas spp. isolated from the suppressive soil of Boukhalef were able to re-establish suppressiveness of this heat-treated soil, suggested their primordial role in the mechanisms of the suppression. Like this, two highly suppressive strains, the nonpathogenic Fusarium oxysporum, strain F6, and Pseudomonas putida, strain Ps4, showed their complementarity in the total establishment of the suppressiveness of the heat-treated same soil. They were also able to induce suppressiveness with more or less efficacy in the others heat-treated suppressive soils.