The formaldehyde-inactivated toxin of corynebacterium diphtheriae. It is generally used in mixtures with tetanus toxoid and pertussis vaccine; (DTP); or with tetanus toxoid alone (DT for pediatric use and Td, which contains 5- to 10-fold less diphtheria toxoid, for other use). diphtheria toxoid is used for the prevention of diphtheria; diphtheria antitoxin is for treatment.