Nineteen well-trained cyclists (14 males and 5 females, mean initial .VO(2max) 62.3 ml kg(-1 )min(-1)) completed a multistage cycle ergometer test to determine maximal mean power output in 4 min (MMPO(4min)), maximal oxygen uptake (.VO(2max)) and maximal accumulated oxygen deficit (MAOD). The athletes were divided into three groups, each of which completed 5, 10 or 15 days of both a control condition (C) and live high:train low altitude exposure (LHTL). The C groups lived and trained at the ambient altitude of 610 m. The LHTL groups spent 8-10 h night(-1) in normobaric hypoxia at a simulated altitude of 2,650 m, and trained at the ambient altitude of 610 m. The changes to MMPO(4min), .VO(2max) and MAOD in response to LHTL altitude exposure were not significantly different for the 5-, 10- and 15-day treatment periods. For the pooled data from all three treatment periods, there were significant increases in MMPO(4min) [mean (SD) 5.15 (0.83) W kg(-1) vs 5.34 (0.78) W kg(-1)] and MAOD [50.1 (14.2) ml kg(-1) vs 54.9 (13.1) ml kg(-1)] in the LHTL athletes between pre- and post-altitude exposure. There were no significant changes in MMPO(4min) [5.09 (0.76) W kg(-1) vs 5.16 (0.86) W kg(-1)] or MAOD [50.5 (14.1) ml kg(-1) vs 49.1 (13.0) ml kg(-1)] in the C athletes over the corresponding period. There were significant increases in .VO(2max) in the athletes during both the LHTL [63.2 (9.0) ml kg(-1 )min(-1) vs 64.1 (9.0) ml kg(-1 )min(-1)] and C [62.0 (8.6) ml kg(-1 )min(-1) vs 63.4 (9.2) ml kg(-1 )min(-1)] conditions. In these athletes, there was no difference in the impact of 5, 10 or 15 days of LHTL on the increases observed in MMPO(4min), .VO(2max) or MAOD; and LHTL increased MMPO(4min) and MAOD more than training at low altitude alone.