Because cell biology has rapidly increased in breadth and depth, instructors are challenged not only to provide undergraduate science students with a strong, up-to-date foundation of knowledge, but also to engage them in the scientific process. To these ends, revision of the Cell Biology Lab course at the University of Wisconsin-La Crosse was undertaken to allow student involvement in experimental design, emphasize data collection and analysis, make connections to the "big picture," and increase student interest in the field. Multiweek laboratory modules were developed as a method to establish an inquiry-based learning environment. Each module utilizes relevant techniques to investigate one or more questions within the context of a fictional story, and there is a progression during the semester from more instructor-guided to more open-ended student investigation. An assessment tool was developed to evaluate student attitudes regarding their lab experience. Analysis of five semesters of data strongly supports the module format as a successful model for inquiry education by increasing student interest and improving attitude toward learning. In addition, student performance on inquiry-based assignments improved over the course of each semester, suggesting an improvement in inquiry-related skills.