The purpose of this investigation was to determine whether the ventilatory gas exchange threshold (Tvent) changes significantly during the first 1-3 weeks of endurance training. Six men were studied during 3 weeks of training, which consisted of pedaling on a cycle ergometer 6 d X wk 30 min per session at 70% of pretraining VO2max. At the end of each week, VO2max, Tvent, and maximal and submaximal heart rates were determined during an incremental exercise test on the cycle ergometer. Constant-load submaximal exercise blood lactate concentrations were determined during training sessions on Monday, Wednesday, and Friday of each week of training. Tvent did not change significantly during the 3 weeks of training (+ 0.091 X min-1; P greater than 0.05). In contrast, significant changes occurred in all other training indexes measured. VO2max increased by 0.36 1 X min-1 (P less than 0.05) after just 2 weeks of training and did not change further after 3 weeks. Significant reductions (40-45%; P less than 0.05) in blood lactate levels during training sessions occurred by the middle of the 2nd week of training. Decreases in maximal (approximately 11 bt X min-1) and submaximal (approximately 14 bt X min-1) exercise heart rates after 1 week of training were significant (P less than 0.05). The results demonstrate that changes in Tvent lag behind alterations in several other cardiovascular and metabolic parameters in response to endurance training.(ABSTRACT TRUNCATED AT 250 WORDS)