This study examines the distribution of properdin factor B by means of electrophoresis on cellulose acetate in a sample of 780 individuals from seven historical/geographical areas of Sardinia: Nurra, Goceano, Nuorese, Arborea, Sarcidano, Ogliastra, Campidano di Cagliari. The gene frequencies obtained for the total sample are BF*S = 0.595, BF*F = 0.227, BF*S1 = 0.012, BF*F1 = 0.166. Division of the total sample into subsamples has highlighted some noticeable differences both among the historical/geographical areas considered and with mainland Italy. In Sardinia relatively low frequencies of the allele BF*S are accompanied by exceptionally high incidences of the variant allele BF*F1, which reaches a maximum in the Goceano area (0.2143).