The individual anaerobic threshold (IAT) as defined by Stegmann et al. 1981 is determined by using the blood lactate-performance relationship during incremental graded exercise and the immediately following recovery phase. The aim of the study was to investigate the validity of the IAT as a measure for the maximum lactate steady state (max Lass) and the monitoring of endurance training. Sixteen endurance trained athletes (VO2max 60.2 +/- 5.0 ml.min-1 x kg-1) performed a stepwise increasing test until exhaustion on a cycle ergometer (CE) (increasing by 50 W every 3 min), 14 endurance trained athletes (VO2max 64.9 +/- 3.8 ml.min-1 x kg-1) performed the multistage steptest on a treadmill (TM) (increasing by 0.5 m.s-1 every 3 min) to determine the IAT and the 4 mmol.l-1 La-threshold (AT). Afterwards endurance tests (E) limited to 30 min (CE) or 45 min (TM) were performed with intensities of 85, 95, 100 and 105% of the IAT (E85-E105) and with 100% of the AT (AT100) (only on CE) in a randomized order each on different days. Lass was present without premature break-off during E85 (in 30 out of 30 cases), E95 (30/30 cases) and E100 (26/30 cases). At E105 and AT100 (104 +/- 7% of IAT) mean La increased continuously and/or led to a premature break-off (in 15/30 cases). All subjects with an AT below their IAT were in Lass during AT100.(ABSTRACT TRUNCATED AT 250 WORDS)