Electromanometric recordings of caecal pressures were made in chronically cannulated ponies. Endoscopy allowed direct observation of the caecal base and cupola while recording intracaecal pressures and enabled a functional interpretation of caecal pressure profiles. Using gas-tight seals, the caecal gas cap baseline pressure (tone) was usually below atmosphere, becoming less negative postprandially. Diurnal variations were observed in the amplitude and frequency of caecal pressure profiles and the direction of caecal movements, during which intra-caecal gas cap pressures briefly became positive. A paraprandial (psychic) phase of enhanced caecal motility was observed. Manipulation of the caecal gas cap volume, by insufflation of nitrogen gas, demonstrated the capacity of the caecal base to regulate gas pressures and to eliminate fermenting gases.