Salmonella typhimurium, Streptococcus faecalis, and enteropathogenic Escherichia coli, which were artificially added to liquid pig manure, and coliforms of the indigenous flora, were reduced by 0·5-2·1 log₁₀ units when subjected to anaerobic filter treatment at 35°C in two pilot-plant reactors. The hydraulic retention times varied between 0·8 and 4·2 days, and reductions decreased with a decrease in this parameter. Reductions apparently followed first-order kinetics. When subjected to separation by gravitation for 24-48 h in small-scale experiments, the liquid fraction of the slurries to be treated by filter digestion contained, on average, up to 0·8 log₁₀ units less of the artificially added bacteria and up to 1·5 log₁₀ units less of coliforms of the indigenous flora. The results of the treatment by anaerobic filter digestion and separation pre-treatment are discussed in comparison with traditional anaerobic digestion at mesophilic temperatures.