Minimal lethal dose

the minimal dose of a toxic substance or infectious agent that is lethal, as assayed in various experimental animals (e.g., the least amount of diphtheria toxin that, on average, kills a 250-g guinea pig within 96 h after subcutaneous inoculation); when followed by a subscript (generally “MLD50”), denotes the minimal dose that is lethal to a certain percentage (e.g., 50%) of animals so assayed