A characterization of gastrointestinal fluids has been performed by means of an electrochemical sensor that has potential for clinical in vivo and in vitro monitoring applications. The sensor comprised a three-electrode cell with a counter, reference, and four working electrodes, Au, Pt, Ir, and Rh. Cyclic voltammetry was used to obtain chemical information from faecal water (in vitro) and gut model (in vivo ) fluids. Stable voltammetric responses were obtained for both fluids at these noble metal working electrodes. The responses differed in shape that demonstrated the discrimination capability and the potential for practical use as a tool for gastrointestinal fluid investigation. The analysis of the stability profiles in faecal water over a 14-h duration has indicated a possible adsorption mechanism with the formation of a biolayer on the sensor surface. The stability in gut model fluids over a 42-h duration has demonstrated a more stable profile, but the mechanisms involved are more complicated to determine.