An extensive sero-epidemiological survey of immunity to tetanus is to be performed in Norway during 1978 and 1979 and thus a simple and reliable method for screening sera for content of tetanus antitoxin is needed. An improved counter-immunoelectrophoretic method for quantification of tetanus antitoxin is described. The toxin neutralization test in mice is considered to correlate well with protection in humans. Counter-immunoelectrophoresis has the advantage of using tetanus toxoid instead of toxin as well as being more rapid and less expensive. Specific antibodies of the IgG, IgM, and IgA classes could be read simultaneously for many sera. This may be of importance, since it is reported in the literature that only antibody of the IgG class is capable of neutralizing tetanus toxin in mice. Counter-immunoelectrophoresis is limited by being less sensitive than the toxin neutralization test in mice.