Blood pressure can be determined more precisely with the use of 24 hours ambulatory measurement in type I diabetics. Nitric oxide (NO) has been suggested to be responsible for the vascular changes described in early diabetic nephropathy. We aimed to investigate serum NO concentration along with ambulatory blood pressure monitoring (ABPM) parameters in type I diabetic patients and to find out whether there are correlation between serum NO level and ABPM parameters. Forty type I diabetic Subjects and 35 controls were enrolled. Diabetic subjects were grouped as microalbuminuric (n=16) and normalbuminuric (n=24). Casual and ambulatory blood pressure parameters and serum NO concentrations were measured in all study population. Microalbuminuric Subjects had higher nighttime systolic blood pressure (SBP), 24 hours diastolic blood pressure (DBP) and 24 hours mean arterial pressure (MAP) than controls. Both microalbuminuric and normalbuminuric Subjects had also significantly higher nighttime DBP and nighttime MAP than controls. Serum NO concentrations were higher in normalbuminuric and microalbuminuric subjects than controls. Serum NO concentrations were positively correlated with daytime DBP and MAP, nighttime SBP, DBP and MAP, and 24 hours DBP and MAP in microalbuminuric subjects. Serum NO concentrations were also positively correlated with nighttime DBP in normalbuminuric subjects. Multiple linear regression analysis revealed that serum NO2-(_)+ NO3- concentrations and 24 hours DBP were independently associated with the development of microalbuminuria. Albuminuria seems to be closely associated with serum NO concentrations and ABPM parameters in type 1 DM patients. A prospective follow-up study on diabetic patients with normo- and micro- albuminuria is needed to confirm the predictive values of increased NO concentrations and ABPM parameters on the development of albuminuria.