Faecal and caecal samples from normal pigs were examined and the factors causing variations in bacterial numbers investigated by a dilution count technique. The range of variation for viable counts of faeces from normal pigs was 1-0 x 106-9.9 x lOo/g and waa in sufficiently close agreement with the results obtained with caecal contents to justify the use of faecal counts aa an index of caecal numbers. The use of individually-fed pigs instead of group-fed pigs, with the consequent reduction of variations in environmental factors, appeared to reduce the variability of the counts. Changes in diet, either by incorporating graas meal or replacing all the animal protein by vegetable protein, did not affect the total numbers of organisms. The small variations in bacterial numbers regarded aa significant by some of the earlier workers thus appear to be of little importance. Smears from high dilutions indicated that the predominant organisms were lactobacilli and streptococci; coli-aerogenes types were present in smaller numbers.