The alkaline lipase in the glyoxysomes from the endosperm of young castor bean seedlings, an integral membrane component, was solubilized in deoxycholate:KCl and purified to apparent homogeneity. The molecular weight on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was 62,000 daltons. The enzyme reaction was markedly stimulated by salts and inhibited by detergents. Triricinolein, the endogenous storage lipid, was hydrolyzed by the purified enzyme which is therefore a true lipase. Treatment of intact glyoxysomes with trypsin strongly diminished the lipase activity but did not affect matrix enzymes. An antibody preparation raised in a rabbit against the purified enzyme inhibited the purified enzyme and that in glyoxysomal membranes.