Thirty-eight strains of the entomopathogenic Beauveria bassiana, isolated from diverse species of Lepidoptera (Pyralidae) or Coleoptera (Curculionidae, Chrysomelidae, and Scolytidae) from various geographical sites, were examined by RFLP and RAPD analyses. Similar groupings were recovered from both approaches and these showed clear relationships between the population structure of B. bassiana and some defined host species. Strains isolated from members of the Pyralidae were recovered as two main groups, one group consisted of all strains isolated from Ostrinia irrespective of their origin. The second group consisted primarily of strains isolated from Diatraea in Cuba. All strains isolated from the curculionid genus Sitona clustered as a single distinct group, separated from strains from other curculionids. In contrast, strains isolated from the pyralid genus Maliarpha, and the coleopteran Chrysomelidae, gave heterogenous patterns and were not recovered as distinct groups. Groups from cluster analysis and non-hierarchic ordination methods were compared and the relative merits of the different grouping strategies are discussed.