Our purpose was to determine initial microbial populations in shredded Iceberg lettuce (Lactuca sativa L.) cv 'Great Lakes', and to study their changes under different controlled atmospheres. Lettuce was shredded, washed, disinfected, water rinsed and centrifuged before being stored for 12 days under air, 3% 02, 3% O2 + 5% CO2 or 3% 0, + 10% CO*. Microbiological analysis and assessment of visual quality were carried out every 3 days. No human pathogens were found. Controlled atmospheres had little or no effect on the microbiological populations studied. A 3% O2 + 10% CO* atmosphere maintained acceptable visual quality of lettuce, without appreciably affecting microbial development.