Abstract
Methods used to detect bacterial contaminants in germ-free laboratory animals are described. Contaminating organisms usually establish themselves permanently in the gastro-intestinal tract but in one instance a species of Corynebacterium was isolated from samples of faeces from a group of rats over a period of five days, after which it disappeared and could not be subsequently isolated. Attention is drawn to changes in management technique which resulted in a marked decrease in the occurrence of contamination.