Major human diseases caused by exotoxins produced by anaerobes include botulisms, tetanus, foodborne illness caused by enterotoxin-producing Clostridium perfringens, and diarrhea/colitis caused by toxigenic Clostridium difficile. Recently, enterotoxigenic Bacteroides fragilis (ETBF) has been recognized, that may be related to childhood diarrheal disease. Detection test of botulinal neurotoxin is hardly performed at clinical laboratories since the most reliable means of detection and identification of botulinal toxin is by using mouse toxicity and neutralization tests. Clinical laboratories should request the tests to a reference laboratory. Since tetanus is easily diagnosed clinically on the basis of its unique, recognizable sings, the bacteriological tests is not usually requested. C. perfringens foodborne illness can be confirmed by testing stool specimens or the suspect food(s) for enterotoxin by the reversed passive latex agglutination test or counting > 10 5 C. perfringens per g of suspected food or > 10 6 C. perfringens spores per g of stool. Diagnosis of C. difficile-associated diarrhea/colitis is confirmed by detection of toxins A or B of C. difficile and/or recovery of toxigenic C. difficile. Isolation of C. difficile strains or detection C. difficile-speciffic antigen from stool specimens is less diagnostic since nontoxic or toxin A positive-toxin B negative strains are prevalent in Japan. Reliable laboratory tests for ETBF-associated childhood diarrhea are not established yet although ETBF can be proved by polymerase chain reaction for detection of the enterotoxin gene.