An elevation of the serum alkaline phosphatase level was found in a patient following resection of a localized jejunal lymphoma. The elevation was due to the presence of Regan isoenzyme of alkaline phosphatase and is assumed to have been produced by the tumor. Following resection of the tumor there was an exponential drop in the level of Regan isoenzyme to undetectable levels 3½ months after surgery. The half-life of the alkaline phosphatase isoenzyme in this case was calculated as ten days. The patient has not shown any recurrence of tumor and the Regan isoenzyme remains undetectable two years after his surgery. This case demonstrates that the finding of an elevated alkaline phosphatase level in a patient with malignancy does not necessarily indicate metastatic disease to bone or liver and should not exclude curative surgery.