In order to know the patogenic behavior of Fusarium oxysporum f. lycopersici, the causal agent of Fusarium wilt of tomato, 48 isolates of the fungus, from different tomato growing areas of the State of São Paulo, Brazil, were tested on the following differential varieties: Bonny Best, Santa Cruz (Kobayashi) and S-34. The inoculation tests were made under gree-house conditions, with partial control of temperature. The results showed that: 1) The fungus may present groups of different patogenicity; 2) 47 isolates belonged to the race 1 of F. oxysporum f. lycopersici; 3)1 isolated showed to belong to the race 2 of the same fungus.