Human gastric lipase (HGL) activity on tributyrin emulsion was detected only in the presence of amphiphiles such as bile salts, proteins (serum albumin, beta-lactoglobulin or ovalbumin) or phosphatidylcholine. These findings are contrary to the strong inhibitory effect of amphiphiles observed on pure pancreatic lipase. To reveal HGL activity, amphiphiles should be added prior to HGL. This may prevent irreversible interfacial denaturation. HGL activity was found to be restricted to a triacylglycerol/water surface tension ranging from 8 dyn/cm to 13 dyn/cm. All amphiphiles, which decrease the interfacial tension below 8 dyn/cm, act as irreversible inhibitors of HGL in the absence and in the presence of bile salts. Our results confirm that HGL is capable of hydrolysing triacylglycerol in the presence of the physiological concentration of bile salts prevailing in the upper small intestine and in the presence of alimentary proteins. These observations could explain the high dietary lipid absorption observed under pancreatic lipase deficiency.