Polyacrylamide gel electrophoresis has been used to separaie the soluble proteins of leaves of perennial ryegrass, harvested before and after exposure to cold hardening conditions. Extracts from plants which had been exposed to low temperatures and short day lengihs contained more soluble protein than extracts of non-hardenedplants. The increase in protein content can be accounted j h r , at least in part, by increases in certain specific, elecirophoretically disiinct, protein fraciions. Similar changes were observed with each of the four varieiies examined.