Cancer antigen (CA 125) is a glycoprotein commonly used as a tumor marker. In this study, CA 125 levels were measured in 149 patients and 26 healthy control subjects. The study group included 69 non-Hodgkin lymphomas (NHL), 25 Hodgkin disease (HD), 20 acute myelocytic leukemia (AML), 14 chronic lymphocytic leukemia (CLL), 12 chronic myelocytic leukemia (CML), and nine multiple myeloma (MM) patients. CA 125 was elevated in 37 of the patients and in none of the control subjects. Average CA 125 level in NHL patients was significantly higher than the controls (56.2+/-9.2 U/ml, 7.99+/-1.05 U/ml respectively) (P<0.05). CA 125 levels were significantly higher in NHL patients with abdominal involvement (113.6+/-23.4 U/ml), with B-symptoms (72.3+/-13.2 U/ml), higher stage of the disease (stages III and IV -75.3+/-14.9 U/ml), bulky disease (99.9+/-30.4 U/ml) and in those with serosal involvement (103.1+/-18.5 U/ml) (P<0.05 for all). CA 125 levels were also elevated in seven patients with HD and in a patient with CLL with pleural effusion. In conclusion, for patients with NHL, high levels of CA 125 were associated with B-symptoms, advanced stage, bulky disease, abdominal, and serosal involvement. Therefore, CA 125 might be used as a marker to predict prognosis and to detect advanced disease in NHL.