This study tested the hypothesis that human pregnancy alters fluid and electrolyte regulation responses to acute short-term exercise. Responses of 22 healthy pregnant women (PG; gestational age, 37.0 ± 0.2 wk) and 17 nonpregnant controls (CG) were compared at rest and during cycling at 70 and 110% of the ventilatory threshold (T_vent). At rest, angiotensin II concentration ([ANG II]) was significantly (P < 0.05) higher in the PG vs. CG while plasma osmolality and concentrations of arginine vasopressin ([AVP]), sodium ([Na⁺]) and potasium ([K⁺]) were significantly lower. Atrial natriuretic peptide concentration ([ANP]) at rest was similar between groups. [ANG II] and [AVP] increased significantly from rest to 110% T_vent in the CG only, while increases in [ANP] were similar between groups. Increases in osmolality, [total protein] and [albumin] from rest to both work rates were similar between the two groups. Pregnant and nonpregnant subjects exhibited similar shifts in fluid during acute short-term exercise, but the increases in ANG II and AVP were absent and attenuated, respectively, during pregnancy. This was attributed to the significantly augmented fluid volume state already present at rest in late gestation.