Alkaline phosphatase was extracted from 5 meningiomas, and several of its biochemical properties were compared with alkaline phosphatase from normal serum and extracts of small intestine. The meningioma phosphatases behaved in a reasonably homogeneous manner. They were virtually uninhibited by 0.05 M L‐phenylalanine and were remarkably heat sensitive. One molar urea produced a similar degree of inactivation to that obtained with alkaline phosphatase of normal serum. Electrophoretically the alkaline phosphatase of all meningiomas produced a single band moving at the same rate as the main band seen in normal serum.