A medical terminological system (TS) is essentially a representation of concepts, attributes and relationships pertaining to medical terms. Although the requirements and structures of TSs have enjoyed some attention in the literature, the actual implementation of TSs consisted so far of ad-hoc approaches starting from scratch. Recently, Protégé has been suggested as a software environment for the development of knowledge-based systems. In Protégé various component types interact, and knowledge can be represented at various levels. This paper investigates how to specify a frame-based TS in Protégé and demonstrates this in a specific application in the intensive care. Our approach is characterized by the utilization of a conceptual framework for understanding TSs and mapping its components onto Protégé constructs. This results in specifications of knowledge components for the implementation of terminological systems. The significance of the work stems from the generality of the specifications, thus facilitating the principled design and development of terminological systems in various medical domains