Exogenous lipase used in the treatment of pancreatic insufficiency may be destroyed by stomach acid. This study was undertaken to search for a readily available source of acid stable lipase. Eleven plant sources (avocado, walnut, pinenut, coconut, lupin, lentils, chickpea, mungbean, oats, castor beans and eggplant) were screened for lipolytic activity using a newly developed radio-isotopic labelled substrate method. The results obtained by this method were confirmed by thin layer chromatography. Two of the sources (castor bean and dehulled oats) showed significant lipolytic activity at pH 5.6, castor beans containing 1.5 U/mg of extracted solid and oats 400-1200 U/mg of extracted solid. Castor beans are difficult to obtain and so may be an impractical commercial source of lipase; however, oats are abundant. If simple methods of enzyme purification and concentration can be developed, oats may prove to be a practical source of acid stable lipase for use in the treatment of patients with pancreatic insufficiency, especially those who have cystic fibrosis.