Bacillus subtilis DNA polymerase III (pol III), an arylhydrazinopyrimidine-sensitive, replication-specific enzyme, was used to generate a non-precipitating rabbit antibody which specifically inhibited pol III activity in vitro. The antibody was used to examine structural relationships among several DNA polymerases, and it was linked covalently to agarose; the antibody:agarose was employed to develop a rapid, selective method of purification of catalytically active B. subtilis pol III.