The Myers-Briggs Type Indicator (MBTI), a measure of personality type and learning style, was used at Saint Louis University in the TRAILS (Tracking Retention and Academic Integration by Learning Style) Project. In addition to considering links between learning styles and student academic achievement and aptitude, MBTI was used to identify discrete academic populations and to assess persistence patterns. MBTI preference indices consist of extraversion/introversion, sensing/intuition, thinking/feeling, and judgment/perception. Certain MBTI learning styles were disproportionately represented in certain academic fields (e.g., the most abstract and reflective learning style was most common in the arts and sciences majors). Performance on aptitude measures differed by MBTI personality types (e.g., students with the most concrete and active style scored lowest). It was also found that the greater the preference for intuition and for introversion, the better the first-term grade point average (GPA), and the greater the preference toward the judging mode, the better the GPA. Using MBTI indicators enables college researchers to assess both proxy measures of social and academic integration and the cognitive and affective processes that influence this integration. (SW)