Young male Sprague-Dawley rats (provided by the Government) will be housed and fed a special diet containing 4% cholesytramine. The rats will be killed, their livers collected and processed to extract fractions containing 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), HMGR kinase, and purified HMGR. The fractions will be deliveredto the Government.