Serum levels of total cholesterol and triglycerides were studied in 202 patients affected by various hematological malignancies at the time of diagnosis. A hypocholesterolemia was found in 44% of patients affected by lymphoproliferative diseases and acute lymphoblastic leukemia, with an evident correlation with the clinical stage (5.7% of patients in nonadvanced stages, 67.8% in advanced stages). In acute and chronic myelo-proliferative diseases, the overall incidence of hypocholesterolemia was 71 %. In particular, a greater incidence of low cholesterol values was found in chronic myeloid leukemia and in idiopathic myelofibrosis than in polycythemia vera. No significant correlation was found in this group of diseases between the values of cholesterol and the main hematological parameters studied (WBC, number of circulating blasts, degree of splenomegaly, levels of hemoglobin, hematocrit). The incidence of significant alterations of triglycerides appeared negligible. It is thus possible to affirm that hypocholesterolemia constitutes an interesting biological aspect in hematological malignancies, and that total cholesterol could represent a parameter, even though secondary, in the follow-up of hematological neoplastic pathologies.