Plants display a series of tolerance mechanism following exposure to low-oxygen stress. Increased secretion of end production of carbohydrate catabolism and synthesis of stress-related proteins are important mechanisms enabling the plant to develop tolerance to anoxia stress. In this study, the secretion of lactate and the activity of plasma membrane H⁺-ATPase in a wild-type (WTS) and a cultivated soybean (CTS) were investigated in response to low-oxygen stress. Low oxygen (0.1% O₂, anoxia) increased the secretion of lactate and reduced the activity of plasma membrane H⁺-ATPase and ATP content in a time-dependent manner. WTS showed greater root elongation and higher survivability than CTS. The higher lactate secretion coincided with the lower accumulation of lactate in WTS than in CTS. Anoxia decreased the cellular pH in soybean roots. Hypoxia (5% O₂) increased the secretion of lactate and the activity of plasma membrane H⁺-ATPase. In comparison to anoxia, hypoxia stress induced increases of 57.4 and 29.7% of endogenous abscisic acid (ABA) in the root apices of WTS and CTS, respectively. Exogenous application of ABA showed a stimulatory effect on the activity of plasma membrane H⁺-ATPase and the secretion of citrate from soybean roots. However, cycloheximide, an inhibitor of protein synthesis, abolished ABA effects. These results suggest that the modulation of the secretion of lactate and activity of plasma membrane H⁺-ATPase in soybean roots is associated with the mechanisms of tolerance to low-oxygen stress. ABA might be involved in the hypoxia signal transmitted in soybean roots.