The present work deals with the studies of variability of Stemphylium solani Weber, the causal agent of gray leaf spot of tomatoes. This disease is becoming very important in all the areas where tomatoes are cultivated. Thirty-three isolates of S. solani were obtained from 12 differents districts of the States of São Paulo. Morphological and phisiological characters such as cultural aspect in PDA and V-8 culture media, sporulation and pathogenicity have been considered. Sporulation varied from one isolate to the others, but the characteristics of each isolate were consistently maintained through resolation from inoculated material and transfers to new media. Two isolates (T-347 and T-419) behaved very differently from the others, both in sporulation and pathogenicity. These isolates sporulated abundantly and spontaneously, and their pathogenicity was significantly higher. Based on the capacity of sporulation in the culture me media, pathogenicity and cultural characteristics the classification of S. solani in 3 physiological races is here pourposed. This classification may help explaning divergent data obtained by other authors. Futhermore, the pathogenic isolates capable of spontaneous sporulation in PDA can be used more properly on tomato breeding programs.