The protein coded by a bleomycin-resistance gene (ble) cloned from producing actinomycetes was purified from a culture of a recombinant E. coli strain and its action on bleomycin was determined by in vitro assays. The protein binds reversibly in a one to one ratio to bleomycin which can no longer cleave DNA. The bleomycin resistance of cells harboring a ble gene could be accounted for by a sequestering effect of the bleomycin-binding protein.