This study was carried out to compare blood lactate changes in isocapnic buffering phase in an incremental exercise test between sprinters and long distance runners, and to seek the possibility for predicting aerobic or anaerobic potential from blood lactate changes in isocapnic buffering phase. Gas exchange variables and blood lactate concentration ([lactate]) in six sprinters (SPR) and nine long distance runners (LDR) were measured during an incremental exercise test (30 W·min^-1) up to subject's voluntary exhaustion on a cycle ergometer. Using a difference between [lactate] at lactate threshold (LT) and [lactate] at the onset of respiratory compensation phase (RCP) and the peak value of [lactate] obtained during a recovery period from the end of the exercise test, the relative increase in [lactate] during the isocapnic buffering phase ([lactate]_ICBP) was assessed. The [lactate] at LT (mean ± SD) was similar in both groups (1.36 ± 0.27 for SPR vs. 1.24 ± 0.24 mmol·l^-1 for LDR), while the [lactate] at RCP and the peak value of [lactate] were found to be significantly higher in SPR than in LDR (3.61 ± 0.33 vs. 2.36 ± 0.45 mmol·l^-1 for RCP, P<0.001, 10.18 ± 1.53 vs. 8.10 ± 1.61 mmol·l^-1 for peak, P<0.05). The [lactate]_ICBP showed a significantly higher value in SPR (22.5 ± 5.9%, P<0.05) compared to that in LDR (14.2 ± 5.0%) as a result of a twofold greater increase of [lactate] from LT to RCP (2.25 ± 0.49 for SPR vs. 1.12 ± 0.39 mmol·l^-1 for LDR). In addition, the [lactate]_ICBP inversely correlated with oxygen uptake at LT (VO₂LT, r=-0.582, P<0.05) and maximal oxygen uptake (VO₂max, r=-0.644, P<0.01). The results indicate that the [lactate]_ICBP is likely to give an index for the integrated metabolic, respiratory and buffering responses at the initial stage of metabolic acidosis derived from lactate accumulation.