Fusarium subglutinans is a maize ear rot pathogen and producer of beauvericin and other mycotoxins. This species has recently been split into two major phylogenetic within-species groups based on RFLP DNA sequence polymorphisms identified in the histone H3 and beta-tubulin sequences. A Pan European collection of the fungus originating mostly from maize was subjected to phylogenetic analysis by RFLP grouping and to chemical analysis for beauvericin production. Of the 62 isolates belonging to Group 1, 48 (77%) produced from 10 to 532 microg/g of beauvericin, whereas none of the 39 Group 2 isolates synthesized detectable amounts of the mycotoxin. The association between RFLP group and beauvericin production is consistent with the existence of two reproductively isolated subgroups within F. subglutinans and indicates that the toxicological risk of isolates of F. subglutinans depends on the group with which they are affiliated.