Increased glomerular filtration rate (GFR) is considered to be a determinant factor in the pathogeny of diabetic nephropathy. In this study we analyzed the effect of a long-acting somatostatin analog (SMS 201-995) on high GFR in type I diabetes patients. Five subjects were involved in a cross-over double blind study. All the patients had a high GFR (205 +/- 18 ml/min/1.73 m2). They were randomly submitted to a 10-hour night i.v. infusion of SMS 201-995 at a rate of 8 g/min and placebo. GFR was measured using a blood 99mTc-DTPA decay curve during the last hour of infusion. After 10-hour SMS 201-995 treatment, no statistical change was observed in GFR. However, a slight decrease was noted in four of the five subjects (183.07 +/- 22.31 vs 202.83 +/- 13.23 ml/min/1.73 m2). GFR was higher only for the patient who presented with a mild hypoglycemic reaction during the infusion, which may increase glomerular filtration by itself. All the other parameters measured remained unchanged.