Serum levels of immunosuppressive acidic protein (IAP) in 17 patients with acute leukemia were measured. The patients included 5 with acute myelocytic leukemia (AML), 4 with acute promyelocytic leukemia (APL), 3 with acute monocytic/myelomonocytic leukemia (AMoL/AMMoL), and 5 with acute lymphocytic leukemia (ALL). Serum IAP levels in untreated acute leukemia patients were higher than those in normal healthy individuals (763.2±321.1 ng/ml vs 389.8±96.7 ng/ml, p<0.05). They tended to decrease to a normal range in complete remission. A correlation was observed between serum IAP levels and the leukemic cell population in the bone marrow (r=0.39, p<0.05). Serum IAP levels increased in febrile patients compared to those in afebrile patients (p<0.05). Patients with more than 500ng/ml of IAP in remission had more risk of relapse in comparison to those with less than 500ng/ml (7 of 10, 70% vs 2 of 15, 13.3%, p<0.05). These results suggest that the measurement of serum IAP is useful for monitoring the leukemic patient
