The erythrocyte (RBC) deformability and lipid composition of RBC membrane were investigated in non-insulin dependent diabetes mellitus (NIDDM) patients (n=20) and healthy controls (n=15). The RBC deformability, whole blood and plasma viscocity were significantly higher in NIDDM patients than in controls (p<0.001). No difference in the RBC count and MCV were found between NIDDM patients and controls. Total cholesterol (TC), total phospholipid (TPL) levels of the plasma were significantly high (P<0.001) and no significant differences were observed in the levels of low density-cholesterol (LDL-C), and high density-cholesterol (HDL-C) in patients with NIDDM compared with the control group. In RBC, TC levels of NIDDM patients were found to be increased (P<0.001) when compared with controls. The levels of TPL did not change in RBC between NIDDM patients and controls. In the plasma and RBC, the ratio of TC/TPL was found to be increased in NIDDM patients compared with control group. A similar trend was observed for RBC phosphatidyicholine (PC) levels, but in this case, the increase was not statistical significantly.