Summary A crude preparation of alkaline phosphatase from bovine intestinal mucosa, obtained by treatment with butanol to release enzyme from the microsomes, was subjected to sequential electrophoresis on starch blocks. The results indicate that the phosphatase may have been present initially in a complexed form and that the complex was disrupted during repeated electrophoretic separation. Such behavior, together with the rather small amounts of enzyme protein which appear to be present in the starting material, may account for some of the difficulties encountered in attempts to purify intestinal alkaline phosphatase. An approximately 260-fold purification was achieved, but the amounts of final product obtained were too small for further study.