Bipolaris sorokiniana is a phytopathogenic fungus that causes diseases of cereal crops, such as leaf-spot disease, common root rot, and black point of grain. Because of its great morphological, physiological, and genetic variability, this fungus is difficult to control. The aim of this investigation was to study the variability of isolates of B. sorokiniana by means of vegetative incompatibility. Thirty-five isolates of B. sorokiniana from different geographical regions in Brazil and other countries were used. The vegetative incompatibility between the isolates and the influences of different culture media on these reactions were evaluated. The total protein profile of the isolates was analyzed when the isolates were cultured separately, and in cultures of compatibility and incompatibility reactions. Eighteen of 31 confrontations showed vegetative incompatibility. The results obtained with different culture media for the vegetative compatibility/incompatibility genotypes suggested that the type of substratum influences these reactions. No differences in protein profiles among the isolates were observed. This result suggests that there is no induction of expression of different proteins in vegetative incompatibility reactions.