During the period January 1975 to August 1977, alkaline phosphatase levels in 30 patients with osteogenic sarcoma were closely followed in an attempt to determine if these measurements had clinical value in predicting the course of patients with this disease. Of 17 patients with elevated preoperative alkaline phosphatase levels, 12 recurred. Of 13 patients with normal preoperative alkaline phosphatase levels, only 4 recurred (p less than .05). Thus, alkaline phosphatase levels that were elevated preoperatively were correlated with poor prognosis. A similar correlation between postoperative alkaline phosphatase levels and prognosis could not be made.