After Zn2+ finger-mediated binding to a DNA break, poly(ADP-ribose) polymerase becomes automodified with long polymers of ADP-ribose. These nucleic acid-like polymers may facilitate DNA repair by noncovalently interacting with neighboring proteins. Using a novel screening technique, we have identified histones as the predominant poly(ADP-ribose)-binding species in human keratinocytes, rat hepatocytes, frog eggs, and yeast. Polymer binding is confined specifically to the histone domains responsible for DNA condensation, i.e. histone tails. Our results indicate that polymers of ADP-ribose are targeted to sites of DNA strand breaks by poly(ADP-ribose) polymerase and subsequently function to alter chromatin conformation through noncovalent interactions with histone tails.