Studies of the chemical characteristics of glomerulopressin were carried out, and the results suggest that glomerulopressin is a glucuronic acid conjugate. Glomerulopressin activity, glucuronide concentration and glomerular filtration rate (GFR), plasma volume (PV), extracellular volume (ECV) and estimated hepatic plasma flow (EHPF), were measured in normal dogs, infused with saline or glucose and in pancreatectomized dogs infused with saline. Glomerulopressin activity, glucuronide concentration and GFR were also measured in pancreatectomized dogs infused with insulin (150 muU/min/kg) through the portal or femoral vein. The glomerulopressin activity, glucuronide concentration and GFR in glucose-infused normal dogs were similar to those observed in saline-infused animals, while they were greatly increased in pancreatectomized dogs. There was no difference between these three groups in PV, ECV, or EHPF. The infusion of insulin through the portal vein of pancreatectomized dogs reduced glomerulopressin, glucuronides and GFR to the values observed in normal dogs, while the infusion on insulin through the femoral vein did not decrease these levels. The increased glomerulopressin produced by pancreatectomy seems to be due to the lack of insulin reaching the liver. The results suggest that pancreatectomy induced an increase of glomerulopressin activity and that this humoral factor increases GFR.