The invention relates to a method for blocking roaming steering mechanisms. According to said method, a foreign cellular device (3), e.g. a cellular telephone, is registered with nationally visited radio network (2) when the foreign (1) and the national cellular network operator have concluded a roaming agreement on mutually debiting cellular services. The invention is characterized in that an anti-roaming steering server (5) installed in the nationally visited cellular network (2) identifies manipulated error messages (14) and selectively manipulates the registration process (8) of foreign mobile users by adequately influencing signaling processes.