The stability of indigenous enteric viruses in samples of settled primary and mixed-liquor activated sludges was studied at 2, 23 and -70 deg C. Changes of virus titer which occurred in these samples were followed during an 84-day observation period, with rates of change then calculated by least-squares regression. Virus survival was found to be statistically dependent (p less than or = to 0.05) upon storage temperature but not sludge solids content. Based upon the observed rates of inactivation, the average times which would be required for a 90 percent decrease in virus titer are 26 days at 23 deg C, 180 days at 2 deg C, and 163 days at -70 deg C. As a group, the rates of virus inactivation observed at 2 deg C were statistically different (p less than or = to 0.05) from those observed at 23 deg C, but not different from those observed at -70 deg C. The three study temperatures were selected to approximate holding of samples in an air conditioned room, on wet ice (H2O), and on dry ice (CO2).