The first phase of the study described was designed in 1986 to investigate why some high-ability minority students follow through with their plans to enroll in college and major in mathematics, science, or engineering (MSE) fields, while others do not. An initial study was succeeded by a first follow-up in 1987, which indicated that minority students persisted in MSE fields to an unusually high degree. A second follow-up was planned and conducted in the 1989-90 academic year through telephone interviews of respondents to the first follow-up questionnaire. The working sample consisted of 5,531 students of American Indian, Black, Mexican American, Puerto Rican, White, and Asian American ethnicity. Results continued to affirm that minority students persisted in MSE fields to an unusually high degree. Persisters were distinguished chiefly by course-selection patterns in high school and college and their personal commitment to MSE. Ethnicity per se contributed little to the prediction of MSE persistence. An appendix describes the telephone tracking procedure. (Contains 1 figure, 22 tables, and 14 references.) (SLD)