The respose of listeria monocytogenes Scott A was examined on exposure to a combination treatment of nisin and modified atmosphere at 4 and 20°C. Atmospheres employed were 100 and 80% CO2/2O% air; and an air control. The organisms were exposed to these atmospheres on raw pork tenderloin treated with various concentrations of nisin (0,l04, and 5 X 104IU/m1)- Treated samples were packaged in PET/A1/PE bags and stored at 4 and 20°C for 30 and 10 days, respectively. Changes in pH9 microbial numbers, gaseous headspace composition, and nisin concentrations were monitored during the storage period. In the absence of nisin, the anaerobic modified at-nmphere (100% CO2) resulted in the failure of both the aerobic plate counts and L. monocytogenes to grow at the temperatures tested. In addition^ both the L. monocytogenes and aerobic vracroorganisim grew in air at 4 and 20°C. In combination with nisin, all atmospheres were inhibitory to the growth of this pathogenic microorganism. These inhibitory effects for MAP/nisin combination system were more pronounced at 4tJ than at 20°C. The combination treatment was also inereasixigly effective with increasing CO2 and nisin concentrations.