TheProtonemura corsicanaspecies group shows an interesting Circummediterranean‐Caucasian distribution, with several relict or insular species. Eight populations belonging to four species of this group and six populations belonging toIsoperla insularis(Morton) were studied by means of electrophoresis, performed on horizontal starch‐gel. Samples were screened for variation at 17 presumptive loci and genetic divergence was calculated. Phenetic treating of allozymic data does not seem to support the theory of a Miocenic colonization of the Mediterranean basin. On the contrary the cladistic approach is not congruent with the phenetic methods and could be in agreement with a Miocenic vicariance hypothesis. Biogeographical patterns based on the systematic arrangement obtained are discussed. The validity of electrophoretic methods in revealing species relationships and boundaries is discussed.