The effects of aerobic and anaerobic digestion on enteric viruses, enteric bacteria, total aerobic bacteria, and intestinal parasites were studied under laboratory and field conditions. Under laboratory conditions, the temperature of the sludge digestion was the major factor influencing survival of bacteria and viruses. Their survival was substantially greater at 7 C than at 28 C. Lowering the temperature or dissolved oxygen level reduced the percentage of solids-associated organisms for bacteria but not for viruses. Bacteria were inactivated at different rates during aerobic sludge digestion. Streptococcus faecalis was more stable than Salmonella typhimurium or Escherichia coli. Varying detention time or source of sludge did not affect the rate of inactivation of viruses or bacteria. Aeration of stock Ascaris suum in sludge reduced percent embryonation and infectivity in rats when compared to aeration in 0.1 N H2SO4.