It has been asserted that the consumption of oxygenated water can support physical working capacity. As this has not been accurately investigated yet we analyzed effects of a two-week period of daily O2-water ingestion on spiroergometric parameters and lactate metabolism in healthy adults. Twenty men (24 +/- 2.5 years of age) with comparable aerobic abilities performed four exhaustive bicycle spiroergometric tests. Applying a double-blind crossover study design 10 subjects drank 1.5 liters of highly oxygenated water every day during the two weeks between the initial two tests whereas the other group consumed 1.5 liters untreated water from the same spring. After a two-week wash-out period subjects underwent a second period consuming the opposite type of water. Spiroergometric parameters and lactate kinetics between both groups at submaximal and maximal levels were analyzed using a MANOVA. Results showed no significant influence on aerobic parameters or lactate metabolism, neither at submaximal nor at maximal levels (all p-values > or = 0.050). Merely increments of VEO2 at submaximal levels were demonstrable (p = 0.048). We conclude that the consumption of oxygenated water does not enhance aerobic performance or lactate kinetics in standardized laboratory testing.