Abstract : This paper presents the specification of the hemodialysis case study, proposed by ABZ’16 conference. The specification was carried out by a coupling of Algebraic State-Transition Diagrams (astd) and B-like methods. astd are a graphical notation, based on automata and process algebra operators. They provide an easy-to-read specification of the dynamic behaviour of the system. The data model is specified using the Event-B language. The system is incrementally designed using extended refinement of both methods.