Pedagogical content knowledge has been defined by Magnusson, Krajcik, and Borko (1999) and others for the purpose of understanding science teachers' knowledge and teaching practice. It is hoped that by improving our understanding of science teachers' PCK, we can improve the education and practice of science teachers. Research describing all domains of a teacher's PCK and its use in the practice of teaching has not been well established. The purpose of this study is to understand how two experienced secondary chemistry teachers' PCK manifests itself in their daily teaching practice. For each teacher, observations, interviews, and class documents were utilized to provide a detailed description of the five domains for PCK as defined by Magnusson et al. Both teachers were well regarded in their schools, but one teacher's PCK was found to be significantly more consistent with our current understanding of science teaching and learning. Along with the comparisons of the two teachers' knowledge, this research found that the teachers' knowledge and their enacted knowledge did not always correspond—suggesting the importance of observations for understanding PCK's influence on teaching practices. In addition, this study supports the importance of clearly defining a teacher's orientation toward science teaching in understanding a teacher's PCK. Both teachers' orientations toward science teaching were found to greatly influence their knowledge and actions in the other PCK domains. Finally, this study suggests that a teacher's knowledge of science curriculum should not be defined only as the knowledge of goals and objectives because this narrow definition of curriculum does not allow a complete understanding of the teacher's knowledge nor how their knowledge affects their practice. These conclusions have implications for future research and teacher educators.