Spores of five type B, five type E, and two type F strains of nonproteolytic Clostridium botulinum were inoculated into tubes of an anaerobic meat medium plus lysozyme to give approximately 10(6) spores per tube. Sets of tubes were then subjected to a heat treatment, cooled, and incubated at 6, 8, 10, 12, and 25 degrees C for up to 60 days. Treatments equivalent to heating at 65 degrees C for 364 min, 70 degrees C for 8 min, and 75 degrees C for 27 min had little effect on growth and toxin formation. After a treatment equivalent to heating at 85 degrees C for 23 min, growth occurred at 6 and 8 degrees C within 28 to 40 days. After a treatment equivalent to heating at 80 degrees C for 19 min, growth occurred in some tubes at 6, 8, 10, or 12 degrees C within 28 to 53 days and at 25 degrees C in all tubes within 15 days. Following a treatment equivalent to heating at 95 degrees C for 15 mine, growth was detected in some tubes incubated at 25 degrees C for fewer than 60 days but not in tubes incubated at 6 to 12 degrees C. The results indicate that heat treatment of processed foods equivalent to maintenance at 85 degrees C for 19 min combined with storage below 12 degrees C and a shelf life of not more than 28 days would reduce the risk of growth from spores of nonproteolytic C. botulinum by a factor of 10(6).(ABSTRACT TRUNCATED AT 250 WORDS)