Research on economic and employment opportunities for men and women has not focused enough on structural features of the labor market. Structural features, which influence worker's capacities to translate their human resources into labor market achievements, include profitability of industries, strength of worker organizations, skill requirements, permeability of labor market boundaries, and occupational sex segregation. A model based on shifts in occupational gender composition can help explain occupational segregation during a period of substantial industrial growth (1870-1900). Such a model can also be extended to other periods. Case histories of approximately 50 occupations (milliners, actors, musicians, journalists, teachers, scientific personnel, potters, for example) during the late 19th century illustrate the hypothesized occupational sex segregation. The model explains this segregation in terms of social definitions of occupations as women's work or men's work, differential acquisition of skills by gender, projected employment stability of males and females, and level of industrialization. On the basis of occupational sex segregation patterns from 1870-1900, it is concluded that present patterns of employment are influenced by the past, high status occupations continue to exclude women, and decreases in occupational segregation will occur only when labor market boundaries are rendered less rigid. (DB)