It has been argued that being able to utilize expertise in discourse is as important as having expertise (C. Candlin and S. Candlin 2002). From a constructivist perspective, knowledgeability does not exist outside of social interaction: being expert involves performing knowledge and skills effectively in social practices (cf. Butler 1990; Lave and Wenger 1991). It is, then, crucial that novice professionals develop the interactional competence to construct themselves as experts in interaction. This study brings together perspectives from research on expert-lay communication, social interaction, and situated learning to examine how a pharmacy intern performed his professional knowledge in the practice of patient consultation over time. Using conversation analysis complemented by the interactional competence framework (Hall 1995; Young 2002), I demonstrate that as the novice pharmacist gained more experience over the course of one internship, he was able to employ professional knowledge in ways that were sensitive to the sequential organization of talk, and to share the patients' lifeworld perspectives (Mishler 1984) more effectively, thus successfully managing the transactional and interpersonal functions of the consultations. This study contributes to research on expert-lay interaction, particularly in pharmacy, and to the under-studied area of interactional competence development in the professions.