The use of the highest scab method for estimating resistance to common scab of parent clones of potato was studied. Under Minnesota conditions, three years of testing appear necessary for estimating clonal resistance by the highest scab method. Clonal resistance of parents was related directly to resistance of progenies. Parents with highest degrees of clonal resistance produced most resistant progenies, those with lower degrees of clonal resistance produced less resistant progenies, and those with no scab-resistant ancestry produced least resistant progenies. Inheritance of resistance to common scab could be explained on a single gene basis with dominance at the duplex level or with the duplex condition necessary for effective clonal resistance.