In crosses of the wild pig (Sus scrofa attila Thomas) with the domestic pig a transferrin variant, Tf I, was detected, electrophoretic mobility of which was slightly faster than the mobility of the variant Tf A. From the results of starch gel electrophoresis, isolation, neuraminidase treatment, autoradiography, and genetic analysis of several families, it can be concluded that the Tf I variant is genetically controlled by the allele Tf1. Thus the number of alleles in the transferrin system of the pig has increased to six (Tf1, TfA, TfB, TfC, TfD and TfE).