Two new histone H2B variants have been isolated from sperm cells of the sea urchin Psammechinus miliaris. They have been designated sperm histone H2B(1) Psammechinus and sperm histone H2B(2) Psammechinus. Both histones are highly homologous to the previously described sperm histones from Parechinus angulosus (Strickland et al. (1977) Eur. J. Biochem. 77, 263--275 and 277--286). The amino acid sequences of the Ps. miliaris sperm histones, though highly homologous, are not identical to the amino acid sequence derived from the codon sequence of a histone H2B gene, characterized from the same organism by Birnstiel et al. ((1977) Nature 266, 603--607).