Short chain fatty acids (SCFAs), such as butyrate, are products of the fermentation of dietary fibres and undigested carbohydrates by anaerobic intestinal microbiota in the human colon. These SCFAs are vital in maintaining the symbiotic relationship that exists between humans and these colonic microbial populations. For example, butyrate induces cell differentiation and regulates growth and proliferation of colonic mucosa (1). A key step in this process is the transport of butyrate into colonic epithelial cells via MCT1 transporters (2). However, the exact cellular localisation of MCT1 protein along the human gastrointestinal tract remains controversial (3;4). Our previous studies have shown MCT1 protein abundance is higher in ascending compared to sigmoid colon (5). The aim of this present study was to investigate the precise MCT1 cellular localization in various human gastrointestinal tissues. Using 10μm sections of paraffin-embedded tissue and an anti-MCT1 antibody, immunolocalization studies confirmed MCT1 protein was strongly detected in the human colon, but not the ileum or stomach. This colonic MCT1 staining was only detected in surface epithelial cells. Further experiments showed strong MCT1 staining in the ascending colon, particularly in the basolateral region of the surface epithelia cells. In contrast, only weaker MCT1 staining was detected in the sigmoid colon and had a more general intracellular distribution within these cells. Finally, strong MCT1 staining was surprisingly also detected in the surface epithelial layers of the foetal colon. These data confirm that MCT1 cellular localization varied along the human gastrointestinal tract. There was also a strong correlation between the strength of MCT1 staining and known levels of bacterially-derived SCFAs present (e.g. strongest signal in ascending colon). Finally, these data highlight the importance of precise tissue location in studies comparing colonic MCT1 abundance between normal and diseased states.