The present invention discloses attenuated Clostridium perfringens organisms that express a substantially nontoxic alpha -toxin. The expressed alpha -toxin is a deletion mutein that relative to the alpha -toxin of the mature alpha -toxin of Clostridium perfringens strain 13, is missing at least nine consecutive amino acid residues including His 68 . The present invention also discloses attenuated organisms that encode the muteins, as well as the use of such attenuated organisms as vaccines.