The complete DNA sequences of two loci encoding H3 and H4 histones in Saccharomyces cerevisiae have been determined. Each locus contains one H3 and one H4 gene. The genes at each locus are divergently transcribed and the coding sequences are separated by 646 base-pairs at one locus and 676 base-pairs at the other. The H3 genes code for identical histone H3 proteins and the H4 genes code for identical histone H4 proteins. The yeast proteins differ from histones H3 and H4 of calf by 15 and 8 amino acid substitutions, respectively, and these differences are largely confined to the carboxy-terminal halves of the proteins. The genes demonstrate a bias in synonymous codon usage similar to that noted for other yeast genes. This bias is confined to the coding sequences of the genes and is specific for the reading frame encoding the proteins. The coding sequence of each gene is flanked on both sides by DNA with an A + T content of 70 to 80%. Possible regulatory sequences are located relative to the 5' and 3'-termini of the histone H3 and H4 RNA transcripts.