This paper compares student headcount enrollment and full-time enrollment prior to and following transition to a semester calendar at 75 public colleges in three state systems: Alabama, Georgia, and Utah. Before and after effects on enrollment in the transition colleges are examined and compared with colleges that did not make the transition. In Alabama, transition colleges experienced net enrollment declines of 5.7 percent and 18.7 percent declines in full-time equivalent (FTE) enrollments over two years; during the same period nontransition colleges experienced increases of 2.7 percent and 1.9 percent, respectively. In Georgia, transition colleges experienced enrollment declines of 1.3 percent and FTE declines of 11.8 percent. Utah experienced enrollment declines of 2.6 percent and 5.8 percent FTE declines; the one nontransition college experienced increases of 13.6 percent and 11.3 percent, respectively. Several reasons are hypothesized for the declines. One is the need to cover the added up-front cost of a longer semester. Another factor is that under the quarter system students were accustomed to taking three five-credit courses and were reluctant to change to five three-hour courses under the semester plan. (Contains 30 references.) (CH)