Pork bellies were formulated to 0, 30, 60, 120, 170, or 340 mug of nitrite per g of meat and inoculated with Clostridium botulinum via pickle or after processing and slicing. Processed bacon was stored at 7 or 27 C and assayed for nitrite, nitrate, and botulinal toxin at different intervals. Nitrite levels declined during processing and storage. The rate of decrease was more rapid at 27 than at 7 C. Although not added to the system, nitrate was detected in samples during processing and storage at 7 and 27 C. The amount of nitrate found was related to formulated nitrite levels. No toxin was found in samples incubated at 7 C throughout the 84-day test period. At 27 C, via pickle, inoculated samples with low inoculum (210 C. botulinum per g before processing and 52 per g after processing) became toxic if formulated with 120 mug of nitrite per g of meat or less. Toxin was not detected in bacon formulated with 170 or 340 mug of nitrite per g of meat under these same conditions. Toxin was detected at all formulated nitrite levels in bacon inoculated via the pickle with 19,000 C. botulinum per g (4,300 per g after processing) and in samples inoculated after slicing. However, increased levels of formulated nitrite decreased the probability of botulinal toxin formation in bacon inoculated by both methods.