['To determine the effects of human immunodeficiency virus (HIV) and highly active antiretroviral therapy (HAART) on oxygen on-kinetics in HIV-positive persons.', 'Quasi-experimental cross-sectional.', 'Infectious disease clinic and exercise laboratory.', 'Referred participants (N=39) included 13 HIV-positive participants taking HAART, 13 HIV-positive participants not taking HAART, and 13 noninfected controls.', 'Participants performed 1 submaximal exercise treadmill test below the ventilatory threshold, 1 above the ventilatory threshold, and 1 maximal treadmill exercise test to exhaustion.', 'Change in oxygen consumption (Delta.VO2) and oxidative response index (Delta.VO2/mean response time).', 'Delta.VO2 was significantly lower in both HIV-positive participants taking (946.5+/-68.1mL) and not taking (871.6+/-119.6mL) HAART than in controls (1265.3+/-99.8mL) during submaximal exercise above the ventilatory threshold. The oxidative response index was also significantly lower (P<.05) in HIV-positive participants both taking (15.0+/-1.3mL/s) and not taking (15.1+/-1.7mL/s) HAART than in controls (20.8+/-2.1mL/s) during exercise above the ventilatory threshold.'] Are impaired oxygen on-kinetics in persons with human immunodeficiency virus due to highly active antiretroviral therapy?