Clostridia are gram-positive, anaerobic, spore-forming rods that are ubiquitous in soil and the intestinal tracts of higher living organisms. The name clostridia is derived from their spindle-shaped appearance (from the Greek kloster = spindle). The pathogenic effect of clostridia is caused by the formation of toxins in the affected animal. Clostridia form exotoxins, some of which are the most powerful biological poisons in the world. Clostridium perfringens type A is found universally in suckling piglets, but the morbidity it causes is a subject of discussion in the farming industry. In the pig industry, particularly, Clostridium perfringens type C is significant as a trigger of necrotic enteritis (NE). Infection with Clostridium perfringens type C, as with E. coli, occurs primarily via the faecal-oral route either directly from the environment or contaminated teats. The majority of the piglets are infected shortly after birth. The production of the ß-toxin leads to the clinical symptoms of NE. The clostridia form spores, which are an extremely resistant dormant form of the bacterium. Under favourable condistions these spores can survive for years in the farrowing crates, as a result Clostridium perfringens type C persists in affected herds.