Women continue to receive fewer doctoral and first-professional degrees than men, even though women receive more bachelor's degrees. The underrepresentation of women holds even after allowing for time to complete an advanced degree. Although researchers have examined sex and racial/ethnic group differences in undergraduate enrollment (e.g., Hurtado, Inkelas, Briggs, & Rhee, 1997; Jackson, 1990; Perna, 2000; St. John & Noell, 1989), few theoretically based, methodologically rigorous studies have explored the sources of observed sex and racial/ethnic group differences in graduate school enrollment using a nationally representative sample of students. This research study contributes to our understanding of the sources of the underrepresentation of women, African Americans, and Hispanics among doctoral and professional degree recipients by examining one phase of the educational pipeline: the enrollment of bachelor's degree recipients in different types of post-baccalaureate educational programs. This study develops and tests a conceptual model that is based on an expanded econometric theoretical framework using data from a nationally representative, longitudinal survey of bachelor's degree recipients. Further, it explores the value of expanding a traditional econometric approach to include measures of social and cultural capital as proxies for individual expectations, preferences, tastes, and uncertainty about the graduate school enrollment decision (Paulsen & St. John, 2002; Perna, 200; St. John & Asker, 2001). (Contains 3 endnotes.)