Serum samples of 683 unrelated male and female individuals of four Sardinian population samples (Sassari, Nuoro, Oristano and Cagliari) were typed for G 1 m (1,2,3,17), G 3 m (5,6,10,11,13,14,15,16,21,26), and Km (1). Phenotype, haplotype (Gm), and allele frequencies (Km), respectively, show a remarkable variability between these four population samples. Comparisons with other Italian populations reveal the considerable genetic difference of the Sardinians, which is in particular caused by the presence of the haplotype Gm1,3;5,10,11,13,14,26 in them. This haplotype is quite uncommon in Europeans and may reflect gene flow from Eastern populations (Phoenicians?) who came to this island in ancient-history times.