In 131 untrained healthy volunteers, unsteady-state upright bicycle ergometry was carried out by means of computer-assisted on-line ergospirometry. In 11 males and 4 females capillary lactate and blood gas analyses sampled simultaneously at 1-min intervals revealed that it is possible to determine the 'anaerobic threshold' (AT) and a 'threshold of decompensated metabolic acidosis' (TDMA) from the respiratory gas exchange by controlling the ventilation equivalent for oxygen (VEO2 = VE/VO2) and carbon dioxide (VECO2 = VE/VCO2). There is no necessity of invasive measurements. Solely ergospirometrical tests in 66 males and 50 females, aged 20--65 years, showed the expected higher work load levels and VO2 at AT and TDMA in males. There was a significant negative correlation to age. In contrast, there are no differences with regard to sex in AT and TDMA for weight-corrected work rates. In the age group 20--39 years, AT is about 1 W/kg body weight, TDMA at about 2 W/kg body weight. The larger maximum exercise capacity weight corrected for males (3 W/kg) in comparison to females (2.6 W/kg) was dependent on a greater capability in the range of maximum exertion and not on a different level of AT and TDMA.