The electrophoretic karyotypes of five strains of Botrytis cinerea from different locations were determined. A unique karyotype was observed for each strain: although general features of the banding pattern of chromosome sized DNA were conserved between strains not two strains had identical karyotypes, indicating that considerable length polymorphism exists in this species. The size of the hands ranged from 1.88 Mb to 3.72 Mb and the genome sizes from 11.22 to 22.49 Mb using chromosomal standards from Hansenula wingeii. Three of the strains were quite similar both in number and size of bands and genome total size and would be the diploid form of the species. The other two presented lower band number and, according to the total genome size, one of them could be haploid and the other an anenploid form. The mitochondrial DNA hand was also shown on gels and its origin confirmed by the cytochrome c oxidase specific reaction. Infection assays were carried out both in Nicotiana tabacum and Vifis uinifera and differences in pathogenicity were shown by the strains, although parasitic degree could not be related to any ploidy state or specific band.