This paper investigates the developing pedagogical content knowledge (PCK) of nine experienced science teachers in their first few years of teaching a new science syllabus in the Dutch secondary education system. We aimed to identify the content and structure of the PCK for a specific topic in the new syllabus, "Models of the Solar System and the Universe", describing the PCK development in terms of relations between four different aspects: knowledge about instructional strategies; knowledge about students' understanding; knowledge about assessment of students; and knowledge about goals and objectives of the topic in the curriculum. Semi-structured interviews were conducted in three subsequent academic years. From the analysis of the data, two qualitatively different types of PCK emerged. Type A can be described as oriented towards model content, while Type B can be typified as oriented towards model content, model production, and thinking about the nature of models. The results also indicate that these two types of PCK developed in qualitatively different ways. (Contains 4 tables and 2 figures.)