Culture filtrates of four enterotoxin-producing strains of Clostridium perfringens type A produced morphological changes in cells of 10 of 12 established mammalian cell lines tested, and particularly Vero (African green-monkey kidney) and MDCK (dog kidney) cells. Double-gel diffusion and Vero-cell tests detected enterotoxin in culture filtrates of, respectively, 29 (28%) and 56 (54%) of 103 strains of C. perfringens tested. The feasibility of cell-culture assays for the routine detection of C. perfringens enterotoxin is indicated.