A procedure in which the chemical or biological activity of a reagent or a living organism is inhibited, usually by a specific neutralizing antibody. As an example, the lethal or the dermonecrotic actions of diphtheria toxin on animals may be completely neutralized by an equivalent amount of diphtheria antitoxin—an antibody produced in animals or in humans after contact with diphtheria toxin or toxoid. Lesser amounts of antitoxin provide intermediate degrees of inhibition. These facts provide the basis for the Schick test for susceptibility to diphtheria. Tetanus and botulinus toxins may be similarly inhibited by their specific antitoxins. In contrast, the typical toxins of dysentery and other gram-negative bacteria are only slightly neutralized, even by large excesses of antibody. Antibodies to bacterial, snake-venom, and other enzyme preparations regularly precipitate them from solution so that the supernates are devoid of enzyme activity; however, the neutralization of activity in the precipitate may range from complete to negligible.