Inflammatory cells, e.g., neutrophils, monocytes, and macrophages are presumed to be a source of circulating phospholipase A in nonpancreatic diseases. Therefore, we investigated in a preliminary study whether serum phospholipase A activity is related to leukocyte counts in 43 patients with hematological diseases. Serum PLA activity was significantly increased in patients with Hodgkin's disease, acute monocytic leukemia, myelofibrosis with myeloid metaplasia, and polycythemia vera when compared with patients with chronic myelogenous leukemia, chronic lymphocytic leukemia, and acute myelogenous leukemia, but did not correlate with total leukocyte counts.