A method of design is presented for logical circuits, starting from worst-case considerations. The method represents an approach to dc optimization. Special attention is paid to temperature and tolerance problems in monolithic integrated circuits. In the worst-case design procedure outlined, the requirements for obtaining a properly functioning circuit are taken as the point of departure. This results in a whole field of possible circuits from which-depending on further specifications-it is comparatively easy to find special solutions. Three examples of worst-case calculations are developed-one for a transistor-transistor logic circuit, one for a diode-transistor logic circuit, and finally, one for a new type of circuit, termed emitter-follower transistor logic.