In teaching science, the beliefs of teachers may come into conflict and inhibit the implementation of reformed teaching practice. An experienced biology teacher, Mr. Hobbs, was found to have two different sets of epistemological beliefs while his classroom practice was predominantly teacher-centered. A case study was then performed in order to investigate the underlying issues that contributed to his classroom practice. Data sources included preliminary and follow-up interviews and classroom observations. Data analysis indicated that factors that prevented the epistemological conflict from reaching a resolution included Mr. Hobbs' beliefs about learning, contextual teaching factors, personal experiences as a student, and views of the nature of science. The findings from this case indicate that science teachers possess complex belief systems that are not immediately obvious to either the teacher or science teacher educators, and science teacher educators need to address teacher beliefs when they encourage teachers to implement reformed teaching practices.