To assess the role played by the large number of rare RFLP variants in producing this result, FsT values for both sets of loci were recalculated after pooling genotypes into three classes: (i) homozygotes for the most common allele, (ii) heterozygotes for the most common allele, and (iii) all other genotypes. The mean FST values determined for the 10 allozyme and the eleven inde- pendent RFLP loci were virtually unaffected by pooling (0.013 and 0.068, respectively), thus eliminating the possibility that the greater number of RFLP alleles led to a spurious elevation in the magnitude of population differentiation observed. No correlation was observed between the degree of heterozygosity of a locus and its FsT value for either the allozymes (T = 0.495, P = 0.146) or the RFLPs (T = 0.256, P = 0.447).