This study is designed to develop an in vitro potency assay to replace the guinea pig death test portion of the official release test for the tetanus component in adsorbed toxoid vaccines. Following published literature, contact was made with the author, and time was spent in his laboratory to learn the mechanics of an Enzyme Linked Immuno Sorbent Assay (ELISA) for guinea pig IgG type antibodies to Tetanus toxin/toxoid. Aliquots of pooled sera from animals tested using the conventional method were set aside for evaluation by ELISA. Responses correlating to the presence of anti-tetanus antibody were measured by ELISA; however, quantitation of the assay, in terms of specific units of neutralizing activity, mg antibody or relative potency to a standard is still under evaluation. Once the method is finalized, collaborative studies are planned.