The coupling of histone and DNA synthesis was examined in the temperature-sensitive hamster fibroblast cell line K12. By monitoring total cellular histone synthesis at various times after quiescent cells were stimulated to proliferate at permissive and nonpermissive temperatures, a direct correlation was found between the rates of DNA and histone synthesis. Furthermore, when DNA synthesis was blocked by the K12 mutation, histone synthesis was reduced to the basal rate.