The article reports on the changes in the full-time workweek in the U.S. from 1900-1970. Between 1900 and 1940, the average workweek of full-time workers declined by 35 percent. The traditional labor market model's shortcomings in explaining the recent trend of the full-time workweek. An estimated annual rate of decline not significantly different from zero was shown. The supply of hours depends on the real wage rate, real asset income and tastes. A generalized least squares estimates of the average workweek in manufacturing as a function of real hourly compensation.