Presumptive mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) were obtained from 54 fungal isolates identified as Verticillium lecanii, V. psalliotae or 'V. lecanii-like'. Analysis of the mtDNA RFLPs showed 20 different patterns, indicating considerable genetic variation within the V. lecanii species complex. There was no direct correlation between host and mtDNA pattern, or between mtDNA patterns and previously described isoenzyme-defined specific groups. Isolates from tropical and subtropical areas showed considerable variation in genotypes, while isolates from temperate regions appeared less variable.