Fusarium oxysporum is one of the most widespread and predominant species in natural and cultivated soils among the fungal genus Fusarium. It includes saprophytes as well as plant pathogens involved in serious vascular wilts, caused by severalformae speciales and races or pathotypes. Morphological similarities among pathogenic and saprophytic strains of F. oxysporum hamper diagnosis and clear discrimination among formae speciales and pathotypes in this species is mainly based on pathogenicity tests. However, the length and cost of such analyses and the fact that pathogenicity can be quantitatively influenced by many environmental and technical variables have prompted the development of alternative molecular methods of characterization in F. oxysporum. With this respect, vegetative compatibility tests, DNA restriction fragment length polymorphisms, isozyme analysis, and electrophoretic karyotyping have been utilized to differentiate many formae speciales of F. oxysporum. DNA random amplification by the use of arbitrarily chosen primers proved most effective in the molecular characterization of Fusarium spp., owing to the ease and speed of the analysis. We report the use of random amplification of polymorphic DNAs (RAPDs) for forma specialis, race and strain determination in pathogenic and antagonistic F. oxysporum.