Allozymes of Paracentrotus lividus from Palermo Gulf in the northern Sicilian coast (Italy) and from a small body-size population in the western Greek coast (Ionian Sea) were investigated by PAGE. Five of the twenty examined loci were polymorphic (AAT*, ADH*, ME*, PGI* and PGM*) over each population with a polymorphism value of 0–25. Average heterozygosity was equal to 0081 in the Sicilian sample and 0084 in the Greek. Deviations from Hardy-Weinberg equilibrium were significant in ME* and PGI* loci (as calculated by y). Nei's (1978) genetic distance (D=0–0025) index described a close identity between the two samples. F ST value of polymorphic loci ranged from 0001 to 0029, its mean value (0–008) resulting low and appearing to be discriminate between the samples with a significant difference (P<0–05). The number of migrants per generation was equal to 31.