Intestinal absorption during infusion (15 ml.min-1) of a 6% carbohydrate (2% glucose and 4% sucrose) solution containing either 0, 25 or 50 mEq.l-1 Na+ was measured by segmental perfusion with a triple lumen tube in males (age 24.3 +/- 1.6) at rest in a neutral environment (22 degrees C). Infusion of the 25 and 50 mEq.l-1 Na+ solutions was performed using a balanced design on the same day, separated by a 1-hr period of no infusion. Infusion of 0 mEq.l-1 Na+ solution was performed on a separate day. A 45-min equilibration period preceded a 90-min test session. Water and solute fluxes were determined from differences in concentration of polyethylene glycol and solute across a 40-cm intestinal segment of the duodenojejunum. A two-factor repeated measures ANOVA indicated no differences (P > 0.1) over time for water, Na+, or glucose flux for all solutions. Plasma volume increased (P < 0.01) approximately 5% over time for all solutions. We conclude that Na+ concentrations of 0, 25, or 50 mEq.l-1 in a 6% carbohydrate solution have similar effects on the absorption of water, Na+, and glucose from the duodenojejunum. Glucose in the infusion solution is the more important factor determining intestinal water absorption than Na+. This study suggests that adding Na+ to fluid replacement beverages may not be a factor in fluid absorption.