Five breeding trials were conducted in an attempt to clarify the mode of inheritance of bovine polydactyly. Two trials involved polydactylous females, superovulation, embryo transfer, and early fetal recovery. The other three trials were father-daughter mating, mother-son mating, and polydactylous X polydactylous matings. The results suggest that the mode of inheritance of bovine polydactylism is polygenic, requiring a dominant gene at one locus and two recessive genes at another locus.