The mode of reproduction of Phaeomoniella chlamydospora (syn.: Phaeoacremonium chlamydosporum) (Pch) and Phaeoacremonium aleophilum (Pal), two mitosporic fungi involved in producing symptoms of esca and a decline of young grapevines, was studied by analysing the amplification profiles obtained in RAPD- and RAMS-PCR experiments (RAPD= Random Amplified Polymorphic DNA; RAMS= Random Amplified Micro- or Mini-Satellites). A low level of polymorphism was found in both species, but no relationship was detected between the genetic variation of isolates and their geographic origin. However, greater variation was found in Pal than in Pch isolates, and more with the RAPD than with the RAMS experiments, as shown by the percentage of polymorphic fragments and multilocus genotypes obtained. The clonal fraction of the Pal and Pch populations, as well as the gametic disequilibrium tests suggested the existence of sexual reproduction in both these species; nevertheless the contribution of asexual reproduction to the genetic structure of the natural populations of Pch seemed to be greater than that of sexual reproduction. With Pal the opposite is thought to be the case.