The authors endeavored to determine: 1) to which physiologic race isolate T-18-1 belongs, previsously identified as race 3 of Fusarium oxysporum f. sp. lycopersici; 2) what type of resistance is present in line CAST-M-Wd, used as a differential in determination of race 3. To attain the objectives desired, 2 experiments were designed in a greenhouse under partial temperature control. In the first experiment the pathogenicity of isolate T-18-1 was determined for 27 progenies of CAST-M-Wd. Variety Walter and line S-34 were used as diferentials since they possess monogenic resistance to races 1 and 2 race 1, respectively. In the second experiment, the pathogenicity of isolate T-18-1 was compared with races 2 of the pathogen. Six progenies of CAST-M-Wd were selected to be used on the basis of results in the first experiment. Variety Walter and line S-34 were used algo. On the basis of the results the following conclusions are drawn: 1) the isolate T-18-1 belongs to race 2 of Fusarium oxysporum f. sp. lycopersici; 2) the tomato line CAST-M-Wd, used previsously as a differential in the identification of race 3, does not possess monogenic resistance but has polygenic resistance to race 3; 3) gene 1-2 in variety Walter demonstrates sufficient resistance for the control of race 2 (isolate T-18-1) as reported in Brazil.