An universal cell (CUSA) permits one to realize any asynchronous automaton by associating such a cell with a state and a connection with a transition. There is no internal variable assignment and all kinds of hazards are avoided. In the first part of the paper we shall present the principle of the CUSA and the synthesis method using flow tables. It is an original method which enables one to reduce the number of cells and useful connections. In the second part, the method is adapted to a synthesis from a flow graph. In this graph, a node is associated with a state, not necessarily a total state, and a branch with a connection. This synthesis method is easy and systematic. CUSA are now being produced by industry and are available as IC's.