Single women dominated the U.S. female labor force from 1870 to 1920. Data on the home life and working conditions of single women in 1888 and 1907 enable the estimation of their earnings functions. Work in the manufacturing sector for these women was task-oriented and payment was frequently by the piece. Earnings rose steeply with experience and peaked early; learning was mainly on-the-job. Occupational segregation by sex was a partial product of the method of payment, and the early termination of human capital investment was a function of the life-cycle labor force participation of these women, although the role of the family was also critical.