A washed whole-cell suspension of bacteria prepared from the faeces of rats regularly fed oral cyclamate incorporated 35S into bacterial protein when challenged with [35s]cyclamate. Control preparations showed low-level incorporation of label. 2. Radioactivity was also accounted for as volatile 35S-containing compounds (s), soluble in sodium hydroxide. 3. Addition of cysteine to incubation mixtures inhibited incorporation of 35S into proteins. 4. The results suggest that the bacterial conversion of cyclamate to the suspected bladder carcinogen, cyclohexylamine, is controlled by the prevailing sulphur metabolism of the intestinal bacteria.
