The present study examines the acute effects of two different exercise intensities on erythrocyte 2,3-diphosphoglycerate (2,3-DPG) concentration. Thirty-one females (X +/- SD age = 23.7 +/- 3.37 yr; VO2max = 44.3 +/- 5.40 ml X kg-1 X min-1) completed 2 separate 15-min constant load cycling tests at exercise intensities representing 35 and 75% of VO2max. Venous blood was obtained pre-exercise (PRE), immediately post-exercise (POST), 15 min post-exercise (POST15), and 30 min post-exercise (POST30) to determine lactic acid, 2,3-DPG, and hemoglobin concentrations and hematocrit. Significant increases (P less than 0.01) in lactic acid concentration (1.1 +/- 0.14 at PRE to 6.2 +/- 0.48 m X mol-1 X l-1 at POST), 2,3-DPG concentration (1.9 +/- 0.06 at PRE to 2.1 +/- 0.06 mumol X ml-1 at POST), and 2,3-DPG corrected for plasma volume shift (PVC 2,3-DPG) (1.9 +/- 0.06 at PRE to 2.4 +/- 0.07 mumol X ml-1 at POST15) were observed only following the 75% submaximal exercise. At POST30 (75% VO2max) PVC 2,3-DPG and lactic acid remained 5.3 and 97% (P less than 0.05) above baseline, respectively. An exercise intensity effect was observed only in lactic acid response (P less than 0.05) but not in 2,3-DPG (mumol X ml-1 and mumol X g-1 hemoglobin or PVC 2,3-DPG. A significant time-intensity interaction (P less than 0.05) for PVC 2,3-DPG suggests that PVC 2,3-DPG response over time was different between the two exercise intensity levels, with the 75% intensity eliciting a greater increase in PVC 2,3-DPG.(ABSTRACT TRUNCATED AT 250 WORDS)