Considerable research has revealed that gut microflora can actively metabolize a wide variety of foreign substances. Among the types of metabolic reactions they may carry out are hydrolysis of glucosides, glucuronides, sulfate esters, amides, esters, sulfamates, and nitrates; dehydroxylation of C- and N-hydroxyl compounds; decarboxylation; dealkyla-tion of o- and α-alkyl compounds; de-halogenation; deamination; heterocyclic ring fission; reduction of double bonds, nitro groups, azo groups, aldehydes, ketones, alcohols, N-oxides, and arsenic acids; aromatization; acetylation; esterification, as well as others (Scheline, 1973). With such a diversity of metabolic reactions, it is not unexpected that these biotransformations by intestinal microflora may have profound toxicological implications.