text: After in vitro labelling of isolated rat liver nuclei, the following ADP-ribosylated and unmodified histones were identified by HPLC and gel electrophoresis: histone H1(0), four histone H1 subfractions, histone H2A.1, histone H2A.2, oxidized histone H2A.2, histone H2A.X, histone H2A.Z, histone H2B, three histone H3 variants and histone H4.