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Recent work in many laboratories [l-8] has confirmed the central role of the arginine-rich histones H3 and H4 in the nucleosome [9]. H3 and H4 occur in solution as the tetramer (H3),(H4)a [lO,l l] and the protein core of the nucleosome probably comprises one such tetramer and two molecules each of the lysine-rich histones H2A and H2B (for references see [ 121 or [ 131). It is generally assumed that those properties of chromatin that are regenerated by reconstitution of DNA and histones H3 and H4 alone, such as nuclease sensitivity [ 11, a low angle X-ray diffraction pattern [6], a beaded appearance in the electron microscope [3-s], and insertion of supercoils into closed circular DNA [3,4,8], are generated by the combination of one tetramer with a nucleosome core length of DNA (about 140 base pairs). However, without better characterisation of reconstituted complexes it is not possible to assess the extent to which a single tetramer is capable of conferring nucleosome-like properties on 140 base pairs of DNA. We report here the preparation and partial characterisation of nucleosome-like particles containing two tetramers of H3 and H4 and about 140 base pairs of DNA; these are distinct from a complex containing one tetramer and 140 base pairs. The particles have been prepared in two ways by mild procedures involving dissociation of the lysine-rich histones from chromatin or nucleosome core particles with salt, thus ensuring minimal manipulation of, and damage to, H3 and H4.