Urea transporters (UTs) encoded by the Slc14a1 (UT-B) and Slc14a2 (UT-A) genes facilitate the movement of urea across plasma membranes. Gastrointestinal urea transporters are thought to play a significant role in the urea nitrogen salvaging process that occurs between mammalian hosts and their gut bacteria (1). UT-A6 has previously been reported in human colon (2) and also in the Caco-2 intestinal cell line (3). Since UT-A gene expression has been shown to be regulated by osmolality (4), the aim of this study was to investigate the role of external osmolality on UT-A6 RNA expression in the human Caco-2 cell line. Initial experiments using end point PCR (RT-PCR) showed human UT-A6 expression in the ascending colon but not the descending colon. Using this RT-PCR, an effect of varying external osmolality was observed when Caco-2 cells were treated for 24 hours with media of different osmolalities – 200, 300 and 600 mOsm. Further experiments using quantitative PCR (qPCR) then confirmed a stimulatory effect of hyperosmolality (i.e. 600 mOsm) on UT-A6 expression (P<0.01, n = 4, ANOVA) as detailed in Table 1. These results confirm the expected regulation of the human UT-A6 urea transporter by external osmolality in Caco-2 cells. The cellular regulatory pathways involved in this process require further investigation. The possible physiological significance of this regulation of hUT-A6 could be related to the increased osmolality of fluid in the ascending colon compared to the sigmoid colon.