This study investigated the breakdown of common histological dyes by anaerobic intestinal bacteria. Nine dyes were selected for this project, each of which belonged to one of four chemical classes. The four chemical classes used were azo, triphenylmethane, phenazotionium, and phenazine dyes. The study required the use of tightly sealed anaerobe culture vessels and an anaerobic gassing apparatus used to evacuate oxygen and fill the culture vessels with nitrogen gas. The anaerobic enteric cultures were first grown in serum vials containing a Tryptose Phoshate broth and a 0.02% concentration of the dye that was tested. Visual changes in the broth inoculated with enteric anaerobes were compared with a control of uninoculated broth. After the visual results were recorded with the use of a camera, the dyes were checked for degradation with the use of spectrophotometry. All of the dyes appeared to have been degraded upon visual inspection but the spectrophotometry showed that only some dyes were degraded. The class of dyes favored for degradation by the intestinal microbes seemed to be triphenylmethane group. Some of the azo dyes showed signs of reduction but the phenazothionium and phenazine groups showed virtually no signs at all.