Fresh chicken breast meals inoculated with Yersinia enterocolitica and Aeromonas hydrophila were packaged in glass jars either containing different compositions of modified atmospheres (MA) (100% CO2; 80% CO2/20% N-2), or in vacuo or containing air, and were stored at 3 +/- 1 degrees C and 8 +/- 1 degrees C. The changes in gas composition as well as Y. enterocolitica, A. hydrophila, total aerobic bacterial, total psychrotrophic, Lactobacilli and Enterobacteriaceae counts were determined after 0, 1, 3, 7, 9, 11 and 14 days of storage. The results show that while the growth of Y. enterocolitica and A. hydrophila were retarded following MA storage, the pathogens were capable of growth in MA and vacuum storage al both temperatures, for the inoculation levels studied. For total aerobic bacterial counts, there were no differences between the values for chicken breast meats kept in different atmospheres. Being packaged in CO2 had the greatest inhibitory effect on the growth of psychrotrophic aerobic bacteria during the first 3 days. Lactic acid bacteria levels of samples stored in MA conditions and in vacuo increased rapidly when compared to those levels of samples stored in air. It was also found that the effect of MA storage increased at 3 +/- 1 degrees C.