A significant diuresis was associated with early sepsis in dogs allowed food and water at will, even though water intake was below or near control levels. This occurred at a time of fever (39.9 C) and of increased fluid losses in the region of inflammation. Acute plasma volume expansion with dextran 75 (Dextran 6%) in normal saline before and after sepsis resulted in a higher peak urine flow 193μl/min/kg) in the septic state than under control conditions (147μl/min/kg). Administration of vasopressin injection during acute plasma volume expansion resulted in a reduction in the diuresis during sepsis (84μl/min/kg), but not under control conditions. Acute pretreatment of animals with desoxycorticosterone acetate (DOCA) was ineffective in dampening the diuresis of sepsis (218μl/min/kg), whereas, chronic treatment (eight days) with DOCA augmented the peak diuresis seen in sepsis (258μl/min/kg) during acute plasma volume expansion. Thus, in this laboratory model, sepsis resulted in an early diuresis, a phenomenon that may be related to a disturbance in the antidiuretic hormone system.