To evaluate the cholesterol metabolism in oncohaematologic patients and its inclusion as a biochemical marker as well as other parameters in the diagnostic period (leukocytes, deshidrogenase lactate, erithrosedimentation, haptoglobine). Many different epidemiological studies discuss the relation between the high risk for cancer mortality and low blood cholesterol in patients with colon, rectum, ovary and brain cancer as well as in chronic myeloid leukaemia, acute leukaemia and policytemia vera.Two groups were studied: a normal group (n = 32) was confronted to a group of oncohaematologic patients (n = 37) (15 lymphoma, 4 acute leukaemia, 7 chronic myeloid leukaemia, 1 chronic myelomonocytic leukaemia, 3 policytemia vera, 5 myeloma and 2 chronic lymphoid leukaemia). In all the cases we determinated the total cholesterol, HDL cholesterol, LDL cholesterol, A1 y B apolipoproteins.The means obtained in the normal group were 184.63 mg/dL, 50.34 mg/dL, 116.38 mg/dL, 140.93 mg/dL, 79.57 mg/dL while in the pathologic group were 163.43 mg/dL, 38.19 mg/dL, 106.60 mg/dL, 102.81 mg/dL and 101.23 mg/dL, respectively. There was a significant difference in the total cholesterol, HDL cholesterol and apolipoprotein A1. These values were lower for leukocytes higher than 10.0 x 10(9)/L. Furthermore the lowest total cholesterol value was seen in myeloma patients.The cholesterol, its fractions and the apolipoproteins determinations might be considered as a biochemical marker while diagnostic is being made, since they are known to play an important role in the tumoral cell metabolism.