Clostridium perfringens is a ubiquitous environmental organism that is capable of causing a variety of diseases in mammals, including gas gangrene and necrotic enteritis in humans. The activity of a secreted hyaluronidase, attributed to the NagH protein, contributes to the pathogenicity of this organism. The family 84 catalytic module of one of the three homologues of NagH found in C. perfringens (ATCC 13124) has been cloned. The 69 kDa catalytic module of NagJ, here called GH84C, was overproduced in Escherichia coli and purified by immobilized metal-affinity chromatography (IMAC). Crystals belonging to space group I222 or I2(1)2(1)2(1) with unit-cell parameters a = 130.39, b = 150.05, c = 155.43 A were obtained that diffracted to 2.1 A. Selenomethionyl crystals have also been produced, leading to the possibility of solving the phase problem by MAD using synchrotron radiation.