The aim of this study was to assess the responses of blood lactate and pyruvate during the lactate minimum speed test. Ten participants (5 males, 5 females; mean +/- s: age 27.1+/-6.7 years, VO2max 52.0+/-7.9 ml x kg(-1) x min(-1)) completed: (1) the lactate minimum speed test, which involved supramaximal sprint exercise to invoke a metabolic acidosis before the completion of an incremental treadmill test (this results in a 'U-shaped' blood lactate profile with the lactate minimum speed being defined as the minimum point on the curve); (2) a standard incremental exercise test without prior sprint exercise for determination of the lactate threshold; and (3) the sprint exercise followed by a passive recovery. The lactate minimum speed (12.0+/-1.4 km x h(-1)) was significantly slower than running speed at the lactate threshold (12.4+/-1.7 km x h(-1)) (P < 0.05), but there were no significant differences in VO2, heart rate or blood lactate concentration between the lactate minimum speed and running speed at the lactate threshold. During the standard incremental test, blood lactate and the lactate-to-pyruvate ratio increased above baseline values at the same time, with pyruvate increasing above baseline at a higher running speed. The rate of lactate, but not pyruvate, disappearance was increased during exercising recovery (early stages of the lactate minimum speed incremental test) compared with passive recovery. This caused the lactate-to-pyruvate ratio to fall during the early stages of the lactate minimum speed test, to reach a minimum point at a running speed that coincided with the lactate minimum speed and that was similar to the point at which the lactate-to-pyruvate ratio increased above baseline in the standard incremental test. Although these results suggest that the mechanism for blood lactate accumulation at the lactate minimum speed and the lactate threshold may be the same, disruption to normal submaximal exercise metabolism as a result of the preceding sprint exercise, including a three- to five-fold elevation of plasma pyruvate concentration, makes it difficult to interpret the blood lactate response to the lactate minimum speed test. Caution should be exercised in the use of this test for the assessment of endurance capacity.