Absorption of fluid by the small intestine of 4-week-old to 12-week-old farmed pheasants and partridges has been studied using an inverted sac technique. The mean rate of absorption was 54±4 (mean±standard error of the mean) μl/g dry tissue/min in pheasants and 49±3 μl/g dry tissue/min in partridges. Use of inhibitors and ion substitution suggested transepithelial transport driven by baso-lateral Na⁺/K⁺ pumps, in combination with mucosal Na⁺-coupled transporters, including Cl^--coupled transporters. Absorption was more than halved to 17±2 μl/g dry tissue/min (P<0.001) in birds that were very heavily infected with Spironucleus spp. in their small intestine and showing a syndrome of diarrhoea, depression and loss of weight to severe emaciation. Birds carrying light to moderate levels of infection with Spironucleus had very variable rates of absorption that were statistically similar to the controls. Doubling the glucose concentration in the buffer to 40 mM significantly enhanced absorption.