1. Changes in the microstructure of histones from the pancreas were followed in rats given ethionine while on a protein-free diet. The lysine-rich histone F1 and the other histones extracted subsequently with 250mm-hydrochloric acid were isolated. When the ethionine-treated rats returned to the stock diet, regeneration of the pancreas was accompanied by an immediate increase in phosphate content of the total histone extract from which histone F1 had been removed. After 3–4 days there was a further increase in the phosphate content of this extract, and also in that of histone F1. 2. Similar changes in the phosphate and thiol+disulphide content of pancreas histones other than F1 were produced by starvation and re-feeding.
