Portuguese populations from localities of sympatry and allopatry of Cicada orni Linnaeus and C. barbara (StÅl), a pair of closely related cicada species, were screened electrophoretically to clarify their genetic relationships. Thirteen enzyme systems coded by 19 presumptive loci were analysed. Seven loci were polymorphic on the 0.95 criterion. Data on within- and between-species variation, based on several genetic estimates (number of alleles per locus, amount of polymorphism, heterozygosity and genetic divergence) are presented. A dendrogram was constructed based on the Cavalli-Sforza & Edwards chord distance, using the UPGMA clustering method. Two groups were produced, one clustering the populations of C. orni and a second one clustering C. barbara. The former cicada species was much more variable genetically than C. barbara, this latter being a very homogeneous species. The high level of genetic similarity might suggest that C. barbara is a relatively recent immigrant to the Iberian Peninsula from its origin in North Africa. Alternatively, the present populations of C. barbara in Portugal might originate from small relict populations having survived the climatic cooling during the ice ages in a few warm refugia. Moreover, the present results suggest that reproductive isolation and therefore speciation in these cicadas may have occurred at a smaller genetic divergence level than in some other insects.