This study was conducted to investigate the values of the order parameter (S) and correlation time (TC) in electron spin resonance spectra for 5-DS (doxylstearic acid) and 16-DS (doxyl-stearic acid) in old normal controls and in patients with type 2 diabetes and stroke in order to assess any association between age-related disorders and membrane FLUIDITY.Materials and Methods: We measured the membrane FLUIDITY (a reciprocal value of membrane microviscosity) of erythrocytes in old healthy controls and in individuals with age-related disorders by using an electron paramagnetic resonance and spin-Iabeling method.The subjects were eleven type 11 diabetic patients (5 males and 6 females) with poor blood glucose (HbA1c 8.48±1.05%), eight old healthy volunteers (4 males and 4 females) with (HbA1c 5.3±1.03%), and ten diabetic stroke patients (5 males and 5 females) with (HbA1c 7.65±1.3). Erythrocyte membrane FLUIDITY was determined by probes, 5- and 16- doxyl-stearic acid methyl ester (SALM) inserted into the erythrocyte membrane bilayer, after which electron spin resonance (ESR) spectra were obtained. Fasting plasma glucose and other blood tests, were measured by standard methods. Results: The order parameter (S) for the spin label agent (5-DS) and the correlation time for 16- DS in the electron spin resonance spectra of erythrocytes were significantly higher in stroke and diabetic patients than in old healthy con trios (OH), indicating that membrane FLUIDITY of erythrocytes was decreased in age-related disorders, compared with old healthy controls. The results indicated the lower levels of erythrocyte membrane FLUIDITY using 16-DS with a motion parameter (p<0.05) but not using 5-DS (p<0.05) in diabetic and stroke patients compared with OH individuals.Conclusion: Use of the 16-DS probe showed a significant decrease in membrane FLUIDITY in patients with Type 2 diabetes and cerebrovascular diseases.