The objectives of this study were to compare in dogs the effects of massive infusion of Ringer's lactate, 5% dextrose in water, and whole blood. Special interest centered upon lung function, central venous pressure, and dilutional effects upon the blood components. Three groups of 5 healthy dogs each received respectively Ringer's lactate, 5% dextrose, or whole blood over 60 minutes in the amount of 135 ml/kg. Arterial blood gases and pH, right atrial and systemic arterial pressures, hemoglobin and hematocrit values, and plasma sodium, chloride, potassium and protein levels were determined. Coagulograms and serum osmolality were examined in the early experiments. The purpose of the whole blood infusion was primarily to serve for comparison in the study of dilutional effects upon blood components. There was no statistically significant change in the arterial blood gas values or pH following Ringer's lactate infusion. The infusion of 5% dextrose in water produced moderate decline in arterial Pco2 and a temporary, slight fall in blood pH. Ringer's lactate infusion produced a prompt and statistically significant rise in central venous pressure. The infusion of 5% dextrose was followed by a late moderate decline in arterial blood pressure, possibly due to marked dilution of plasma sodium, chloride and potassium. It is concluded that massive Ringer's lactate infusion is capable of increasing right atrial pressure and presumably cardiac output. In healthy dogs, lung function was not impaired sufficiently to alter arterial blood gas values. However, where other previous or concomitant factors have diminished pulmonary reserve, fluid overload may impose a serious additional burden upon cardiopulmonary function.