To assess the relationship of exercise test variables to each other and to bike race times in an ultra-distance triathlon, we studied 24 participants (14 men, 10 women) in the 1985 Hawaii Ironman Triathlon, using a graded, maximal cycle ergometer test with gas exchange and blood lactate (LA) measurements at each work load. Exercise test variables were oxygen uptake (VO2) and heart rate (HR) at the lactate and ventilatory thresholds. Lactate threshold (LT-1) was defined as the exercise intensity that elicited a 1 mM increase in blood lactate concentration above the value measured during the first work load for each subject. Variables were also examined at the lactate thresholds of 2 mM and 4 mM. Ventilatory thresholds (VT) were identified as the points at which the ventilatory equivalent of oxygen (VE/VO2) increased without a corresponding increase in the ventilatory equivalent of carbon dioxide (VE/VCO2). Mean peak oxygen uptake (peak VO2) for this sample of Ironman triathletes was 57.4 ml.kg-1.min-1. Cycle peak VO2 was inversely correlated, r = 0.68 (P less than 0.0002) with bike finish time. VO2 and HR as well as the respective percentages of maximum were higher at all lactate thresholds than at VT (P less than 0.0001). Therefore VT should not be used to identify a lactate threshold in ultra-endurance triathletes. VO2 values at the lactate and ventilatory thresholds were not highly related to bike finish time (r = -0.26 to -0.58). Fractional utilization of peak VO2 (% peak VO2), HR, and % peak HR at thresholds were not related to bike finish time (r = -0.01 to 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)