The purpose of this study was to investigate how science faculty members' belief systems about inquiry-based teaching changed through their experience in a professional development program. The program was designed to support early career science faculty in learning about inquiry and incorporating an inquiry-based approach to teaching laboratories. Data sources for this qualitative study included three semi-structured interviews, observations during the program and during faculty members' implementation in their courses, and a researcher's journal. In the first phase of data analysis, we created profiles for each of the four participants. Next, we developed assertions, and tested for confirming and disconfirming evidence across the profiles. The assertions indicated that, through the professional development program, participants' knowledge and beliefs about inquiry-based teaching shifted, placing more value on student-directed learning and classroom inquiry. Participants who were internally motivated to participate and held incoming positive attitudes toward the mini-journal inquiry-based approach were more likely to incorporate the approach in their future practice. Students' responses played a critical role in participants' belief systems and their decision to continue using the inquiry-based format. The findings from this study have implications for professional development design.