Abstract: An assay for the identification of neutralizing botulinum antibodies in sera is provided which includes the steps of separating non-sodium dodecyl sulfate, non-trypsinized complex botulinum toxin in an arylamide gel by electrophoresis, the separation occurring on a basis of botulinum toxin protein size and charge. Thereafter, the separated protein is electrophoretically transferred onto a solid support, the transferred separated protein being bound to the solid support at spaced apart sites. Remaining sites on the solid support not occupied by bound protein are blocked and the solid support and bound protein are contacted with a sera sample containing an antibody directed against botulinum toxin. The contacted solid support is then exposed to a second antibody capable of reacting to produce an insoluble colored substrate of intensity relative to a quantity of antibodies present. Finally, the second antibody is reacted to produce the insoluble colored substrate which is visually identified.