The Home Blood Pressure for Diabetic Nephropathy (HBP-DN) study is a prospective cohort study to determine the optimal home blood pressure (HBP) required to improve the prognosis of type 2 diabetic patients with microalbuminuria. The glomerular filtration rate (GFR) is heterogeneous in microalbuminuric diabetic patients. The first step of the HBP-DN study explored the significance of estimating GFR for the identification of patients for whom HBP measurement would be more helpful. The patients were divided into two groups based on their estimated GFR (eGFR): a low eGFR group (eGFR <60 ml min(-1) per 1.73 m(2), N=75) and a preserved eGFR group (eGFR 60 ml min(-1) per 1.73 m(2), N=193). HBP, variability of HBP and a previous history of vascular complications were compared between the two groups. The number of antihypertensive drugs used for the patients and the s.d. of home systolic blood pressure (HSBP) in the low eGFR group were significantly higher than those in the preserved eGFR group. A stepwise multiple linear regression analysis also revealed that the low eGFR group was independently correlated with the s.d. of HSBP. A multiple logistic regression analysis revealed that a low eGFR was an independent risk factor for coronary heart disease and advanced retinopathy. Estimating the GFR is important to identify patients with elevated blood pressure variability, as well as those with a high risk of vascular complications. Measuring HBP would be more helpful for the effective and safe treatment of hypertension in patients with a low eGFR than in those with a preserved eGFR.