Peripheral blood leukocyte alkaline phosphatase (LAP) scores and CA15- 3, CA125, and CEA levels in plasma were measured in 57 patients with metastatic breast, ovarian, and colorectal cancer, respectively, and in 79 patients with the same types of nonmetastatic cancer. The mean LAP scores of the metastatic cancer patients (261, 272 and 275 for breast, ovary and colon, respectively) were significantly higher than those of the nonmetastatic cancer group (70, 68 and 57, respectively). There was no overlap between the 95% confidence intervals of the two groups (i.e., metastatic versus nonmetastatic), and no patient known to be metastatic had a LAP score within the normal range. The mean levels of other markers in the metastatic patients (CA15-3, 63.4 μ/ml; CA125, 104.8 μ/ml; and CEA, 51.8 ng/ml for metastatic breast, ovarian, and colon cancer, respectively) were also higher than in the nonmetastatic patients (CA15-3, 24 μ/ml; CA125, 25.3 μ/ml; and CEA, 5.8 ng/ml for nonmetastatic breast, ovarian, and colon cancer, respectively). However, the 95% confidence intervals of the nonmetastatic and the metastatic patients overlapped so that there were false-negatives and/or false-positives when the other markers were used. We therefore conclude that the addition of the LAP score to conventional cancer markers could be helpful for the diagnosis of recurrence and follow-up of cancer patients and suggest that our results be confirmed by further studies on a larger series of patients.