The association of newly synthesized histones with newly replicated versus non-replicating DNA is under investigation. Three separate approaches are taken: 1) density labeling DNA with 14C-BUdR, radiolabeling chromatin proteins with 3H-arginine, and determining the coincidence or non-coincidence of the two isotopes in buoyant density gradients; 2) pulse-labeling chromatin proteins and determining whether the new proteins band with total chromatin or the replication satellite; and 3) measurement of the kinetics of digestion and size of the particles containing pulse-labeled histones to determine whether these parameters follow the parental chromatin profile or the newly replicated chromatin profile.