The causal relationship between VE/VCO₂ and the acid base state during high intensity exercise is a matter of debate. 58 subjects performed endurance tests with an intensity of 80% of maximum power (cycle ergometer). Spirometric data were measured with the Metalyzer 3B breath by breath. [Lac] concentrations in arterialized blood were determined. The respiratory data were fitted to an exponential equation with a linear term. During high intensity exercise the amplitude of VE and VCO₂ did not show any significant correlation with [Lac] in the 3rd min of exercise. The linear term of the VE and of the VCO₂ kinetics did not correlate with the concomitant increase of [Lac]. The amplitudes and the linear terms of the VO₂-kinetics correlate significantly with that of VCO₂ (p<0,001), however, the amplitude of VCO₂ was 25% larger than that of VO₂ and the linear term of VCO₂ is less than 50% of that of VO₂. That shows that at the beginning of exercise, when [Lac] is low, CO₂ is exhaled in excess. If exercise is prolonged, in spite of the increasing [Lac] and the increasing VE, less than the produced CO₂ is exhaled. Thus the interpretation, that the increase in arterial [Lac] increases VE and VCO₂ to compensate for the metabolic acidosis has to be questioned. VE might be influenced by the strain and thus centrally regulated.