Desquamation rate of jejunal epithelial tissue was studied in fasting cats by measuring the rate of accumulation of DNA in the luminal fluid. The applicability of the method was first determined by calculating a turnover time for the tissue from the rate of accumulation of DNA and comparing it with turnover time calculated by the colchicine method. The two values agreed. When female cats were fasted, desquamation rate decreased progressively during 256 h without change in epithelial cell mass. Changes in des quamation rate may play an important role in the response of intestinal mucosa to changes in quantity of food intake.