The sensitivity of genetic fingerprinting rests in the ability of the procedure to detect the rare or subtle differences that exist between the genes of one individual and another. In a typical experiment, discrete subsets of the genetic material (DNA) of two or more organisms are analysed for genetic similarities and differences, and calculations are made as to the likely relatedness of the organisms based on the observed genetic similarity. In the present investigation, we have applied the RAPD-PCR technique 1 to strains of V. dahliae isolated from cotton plants from a range of production regions in Australia. By using genetic fingerprinting to identify different strains of V. dahliae, we hope to achieve a better understanding of the epidemiology of Verticillium wilt disease in cotton.