Aerolysin is a major virulence factor produced by the Gram-negative bacterium Aeromonas hydrophila and is a member of the beta-pore-forming toxin family. Two oligomerization-deficient aerolysin mutants, H132D and H132N, have been overproduced, proteolyzed by trypsin digestion and purified. Crystals were grown from the proteolyzed forms and diffraction data were collected for the two mutants to 2.1 and 2.3 A resolution, respectively. The prism-shaped crystals belonged to space group C2. The crystal structure of the mutants in the mature, but not heptameric, aerolysin form will provide insight into the intermediate states in the oligomerization process of a pore-forming toxin.