Cans of chopped ham, inoculated with spores of Clostridium botulinum strains 33A and 41B at levels of 2,500 and 250 per gram, were subjected to an enzyme-inactivating heat treatment and irradiation with 0.5, 1.5, 2.5, or 3.5 Mrad of Co(60). A portion of the pack was not irradiated, and received a commercial thermal process (F(0) = 0.2). Viable spores were enumerated after treatment and after 6 months of incubation at 30 to 37.7 C. Toxic spoilage occurred at 0 and 0.5, but not at 1.5, 2.5, or 3.5 Mrad. More spoilage and toxin formation occurred in the product irradiated at 0.5 Mrad than in identical product receiving no radiation treatment. Confirmed botulinal spores were isolated from all of the radiation variables of 2,500 per gram-inoculated product and from all but the 3.5 Mrad low-inoculum cans. However, neither growth nor toxin was observed in unspoiled product. The "injury" phenomenon previously described in thermally processed cured meats (survival of botulinal spores without capacity for multiplication or toxigenesis) apparently occurs also in irradiated cured meats.