This article surveys research activities in on-line hardware-checking techniques developed in Eastern Europe including the former Soviet Union. It presents some interesting results on self-checking circuit design, many of which are unknown to Western researchers as they appeared in not-so-widely known journals and conference proceedings. Much of the work is new and is judged to be a significant contribution to the field. Among the traditional designs intended for synchronous circuits are some state-of-the-art self-testing checkers, new error detecting unordered codes that are an extension of Berger codes, self-checking combinational circuits using parity, and several designs of totally self-checking synchronous sequential circuits. Included also are the first-ever design concepts of totally self-checking asynchronous circuits.