Linearized unit length DNA obtained after cleavage of the supercoiled DNA of the human papovavirus BKV by PstI (0.31) induced transformation and T antigen less efficiently than DNA cleaved by EcoRI (0.0), BamHI (0.98), KpnI (0.90) or HhaI (0.73). BKV DNA cleaved by XbaI (0.27 and 0.95) did not induce T antigen.