The aim of this study was to determine whether V˙O2 kinetics and specifically, the time constant of transitions from rest to heavy (τ p H) and severe (τ p S) exercise intensities, are related to middle distance swimming performance.Fourteen highly trained male swimmers (mean±SD: 20.5±3.0yr; 75.4±12.4kg; 1.80±0.07m) performed an discontinuous incremental test, as well as square wave transitions for heavy and severe swimming intensities, to determine V˙O2 kinetics parameters using two exponential functions.All the tests involved front-crawl swimming with breath-by-breath analysis using the Aquatrainer swimming snorkel. Endurance performance was recorded as the time taken to complete a 400m freestyle swim within an official competition (T400), one month from the date of the other tests.T400 (Mean±SD) (251.4±12.4 s) was significantly correlated with τ p H (15.8±4.8s; r=0.62; p=0.02) and τ p S (15.8±4.7s; r=0.61; p=0.02). The best single predictor of 400m freestyle time, out of the variables that were assessed, was the velocity at V˙O2 max vV˙O2 max, which accounted for 80% of the variation in performance between swimmers. However, τ p H and V˙O2 max were also found to influence the prediction of T400 when they were included in a regression model that involved respiratory parameters only.Faster kinetics during the primary phase of the V˙O2 response is associated with better performance during middle-distance swimming. However, vV˙O2 max appears to be a better predictor of T400.