Abstract Experiments were designed to study the effect of various modified atmospheres (MA) on the survival rate of hepatitis A virus (HAV) on lettuce. Pieces of lettuce inoculated with HAV were incubated at room temperature (RT) and 4°C for 12 days in ambient air and under various modified atmospheres (CO2:N2at 30:70, 50:50, 70:30 and 100% CO2) inside plastic bags of low O2permeability. Samples were removed on days 1, 3, 6, 9 and 12 and the virus was recovered and plaque-assayed to determine residual titer. Incubation for 12 days at 4°C showed that the lowest HAV survival rate (47·5%) was on lettuce stored in a petri-dish (atmospheric air), whereas the greatest survival rates (83·6%) was on lettuce stored under 70% CO2. Statistical analysis of virus survival at 4°C indicated that HAV titers decreased for all packages, but without a significant (P>0·05) difference between the package types. At RT, however, a significantly (P