The rat testis chromatin fractions (soluble, S, and insoluble, P) were prepared by mild digestion of riuclei with DNAase I. They appeared to be different in specific biochemical features such as their transcriptional compe:ence and protein patterns, the latter indicating, according to results previously obtained, that the testis-specific H 1 t is preferentially associated to the soluble fraction, whereas the other H I variants are localized in the pellet. S and P chromatins also differed in the distribution of the poly(ADP-ribosybating system, (poly(ADP-ribose)polyrnerase, reaction product and acceptor proteins), detected by incubating nuclei with 32P-NAD. The 32P-modified H I s and core histones of both fractions, known as specific ADPribose target proteins, were separated by high performance liquid chromatography and it was demonstrated that the H I variants from S and P are differently ADPribosylated, being H l t always the best acceptor, and that most of the ADPribosylated variants were solubilized after DNase I treatmeni. The further digestion of P chromatin with the nuclease produced a fraction (pP) devoid of most DNA, but partic.ilarly enriched in transcriptionally competent tracts. The low DNA content of pP chromatin, which reflects the typical feature of a nuclear matrix, corresponded to a relevant poly(ADPribosyl)ation, the highest as compared to S and P fractions. Moreover, long and branched chains of poly(ADP-ribose) were found associated to pP sample which resemble the products determined in the soluble chromatin.