This paper presents two South African case studies designed to explore the influence of subject matter knowledge on pedagogical content knowledge (PCK). In the first case study on teaching the mole in two township schools, the findings illustrate that the participant teachers favoured procedural approaches at the expense of conceptual understanding. The second case study examines the teaching of chemical equilibrium to students on a bridging programme in a tertiary institution. Through these data, the authors present a model to assist in understanding the amalgamation of subject matter knowledge (SMK) with other teacher knowledge domains to produce what we describe as "manifestations." The model was useful in interpreting the teachers' practice, especially to highlight the role of SMK, and therefore offers interesting insights into the nature of PCK and its influence on science teaching. (Contains 3 figures and 4 tables.)