As a prerequisite for the synthesis of affinity labels, we describe methods to couple histones to ribonucleic acids. For the synthesis of these covalent hybrid molecules, we used a population of histones H1, H2A, H2B, H3, and H4 from calf thymus and polyadenylic acid with an average chain length of up to 260-280 bases, representing the size of poly(A)-tails from mature mRNAs. Three methods were investigated. (a) Poly(A) containing an 8-N3-A residue was cross-linked to histones by ultraviolet irradiation. (b) The 3'-end of the polynucleotide was connected to a mononucleotide containing an aliphatic amino group, and the resulting poly(A)-derivative was coupled to histones via derivation with a bromoacetyl group. (c) The 3'-end of the polynucleotide was oxidized with sodium periodate and bound covalently to an amino group of the polypeptide. To demonstrate the RNA content of the hybrid molecule, the poly(A) was removed with RNase T2.