A lecture section of introductory biology that historically enrolled more than 500 students was split into two smaller sections of approximately 250 students each. A traditional lecture format was followed in the "traditional" section; lecture time in the "active" section was drastically reduced in favor of a variety of in-class student-centered activities. Students in both sections took unannounced quizzes and multiple-choice exams. Evaluation consisted of comparisons of student survey responses, scores on standardized teaching evaluation forms, section averages and attendance, and open-ended student comments on end-of-term surveys. Results demonstrate that students perform as well, if not better, in an active versus traditional environment. However, student concerns about instructor expectations indicate that a judicious balance of student-centered activities and presentation-style instruction may be the best approach. (Contains 4 tables and 2 figures.)