In recent years, there has been a growing interest in the knowledge base of prospective science teachers. An important part of their pedagogical content knowledge (PCK) consists of concerns about teaching. Most of the research on these concerns is focused on rather general teaching issues, and little is known about their concerns dealing with teaching specific science issues. This paper presents an exploratory study of prospective teachers' concerns about teaching a central issue in science: linking macroscopic phenomena with microscopic particles and symbolic representations such as formulas and equations. Teaching this issue evokes a lot of students' conceptual difficulties, and for that reason, may evoke pedagogical content concerns (PCC) among prospective teachers. In this naturalistic case study, prospective teachers (n=8) were interviewed before and after the first two weeks of lessons about relevant topics at a macro-micro symbolic interface. The semi-structured interviews and the lessons were audiotaped and analyzed. The results reveal a number of important characteristics of the nature of the development of prospective science teachers' PCC. Implications of the study for science teacher education are discussed. Contains 30 references. (Author/WRM)