The effects of packaging atmosphere (aerobic, vacuum, MAP, or MAP-CO) on pork chops were investigated. Eighty pork loins (40 injected, 40 uninjected) of normal inherent muscle quality were used to evaluate the color, microbial growth, rancidity, purge, and sensory quality of pork chops in four different packaging environments during refrigerated storage. All treatments were evaluated 3 times/week for 5 weeks during storage at 0-20C. Hunter a* values (for both injected and uninjected chops) were significantly (P< 0.001) higher in MAP-CO (11.25) than the aerobic (6.93), MAP (3.80), or the vacuum (2.74) packages. Sensory evaluations supported this, as color values (100 point scale) were also higher for chops in MAP-CO (85.91) than aerobic (62.47), MAP (42.42), and vacuum (44.52) packages. Rancidity (TBARS) was significantly (P< 0.001) reduced during storage by MAP-CO (0.118) as compared to the aerobic packages (0.365). However, MAP-CO did not significantly reduce microbial growth or purge loss. The results showed that carbon monoxide significantly improved color stability and sensory characteristics of pork in modified atmosphere packages during refrigerated storage.