Basidiospores of the Basidiomycete Psilocybe mutans have been found to germinate only in the presence of water extracts of animal dung. The chemical nature of the factor present in the dung that induces germination is not known, nor has it ever been isolated· Experiments showed that extracts of bile salts cause the basidiospores to germinate, indicating that since bile salts are found in dung, they may be the factor which stimulates the spores to germinate. Investigations of the properties of the factor in dung show that the factor has solubility properties that are similar to those of the bile acids. It was found that the bile salts are able to stimulate the germination of the spores optimally at a concentration that corresponds to the critical micellar concentration of the bile salts. This suggests that the bile salts activate the germination due to their surface active properties.