Undergraduate biology education is often viewed as being focused on memorization rather than development of students' critical-thinking abilities. We speculated that open-note testing would be an easily implemented change that would emphasize higher-order thinking. As open-note testing is not commonly used in the biological sciences and the literature on its effects in biology education is sparse, we performed a comprehensive analysis of this intervention on a primary literature--based exam across three large-enrollment laboratory courses. Although students believed open-note testing would impact exam scores, we found no effect on performance, either overall or on questions of nearly all Bloom's levels. Open-note testing also produced no advantage when examined under a variety of parameters, including research experience, grade point average, course grade, prior exposure to primary literature--focused laboratory courses, or gender. Interestingly, we did observe small differences in open-and closed-note exam performance and perception for students who experienced open-note exams for an entire quarter. This implies that student preparation or in-test behavior can be altered by exposure to open-note testing conditions in a single course and that increased experience may be necessary to truly understand the impact of this intervention.