Clostridium perfringens type A is the most common cause of poultry necrotic enteritis (NE). Of the four “major” toxins, type A strains produce only alpha toxin (CPA), which has long been considered a major factor in pathogenesis of NE. We investigated the virulence for poultry of type A strains from a variety of enteric sources. Newly-hatched Cornish × Rock chicks were fed a low protein diet for one week, a high protein diet for a second week, and then challenged with log-phase cultures of C. perfringens, mixed 3:4 (v/v) with high protein feed. Strain JGS4143 [genotype A, beta2 positive ( cpb2 pos), from a field case of NE] produced gross lesions compatible with NE in >85% of challenged birds. However, strains JGS1714 (enterotoxigenic genotype A, cpb2 pos, human food poisoning), JGS1936 (genotype A, cpb2 neg, bovine neonatal enteritis), JGS4142 (genotype A, cpb2 pos, bovine jejunal hemorrhage syndrome), JGS1473 (genotype A, cpb2 pos, chicken normal flora), JGS1070 (genotype C, cpb2 pos, porcine hemorrhagic enteritis), JGS1882 (genotype A, cpb2 pos, porcine neonatal enteritis), JGS1120 (ATCC 13124, genotype A, cpb2 neg, gas gangrene), JGS4151 (strain 13, genotype A, cpb2 pos, canine), and JGS4303 (SM101, enterotoxigenic genotype A, cpb2 neg, human food poisoning) failed to produce disease. In vivo passage failed to increase virulence of the non-NE strains. NE strains must have specific poultry-associated virulence attributes, such as the recently identified NetB and other factors, which allow for the development of disease.