The purpose of this study was to investigate the validity of the ventilatory response during incremental exercise as indication of endurance performance during prolonged high-intensity exercise under field test conditions in elite cyclists. The ventilatory threshold (VT) was assessed in 14 male elite cyclists (age 22.4+/-3.4 years, height 181+/-6 cm, weight 69.2+/-6.8 kg, VO2max 69+/-7 ml x min(-1) x kg(-1)) during an incremental exercise test (20 W x min(-1)). Heart rate and oxygen uptake were assessed at the following ventilatory parameters: 1. Steeper increase of VCO2 as compared to VO2 (V-slope-method); 2. Respiratory exchange ratio (RQ)=0.95 and 1.00; 3. VE/VO2 increase without a concomitant VE/VCO2 (VE/VO2 method). Three weeks following the laboratory tests, the ability to maintain high-intensity exercise was determined during a 40 km time trial on a bicycle. During this time trial the mean heart rate (HR(TT)) and the road racing time (TT) were assessed. The V-slope-method and the VE/VO2 method showed significant correlations with TT (V-slope: r = -0.82; p<0.001; 90% interval of confidence = +/-82 sec; VE/VO2: r=-0.81; p<0.01; 90% interval of confidence = +/-81 sec). Heart rate at the ventilatory parameters and at the maximum heart rate (HRmax) showed significant correlations with HR(TT). The V-slope-method is the preferred method to predict heart rate during prolonged high-intensity exercise (r=0.93; p<0.0001; 90% interval of confidence: +/-4.8 beats x min(-1)). For predicting heart rate during prolonged high-intensity exercise using an incremental exercise test (20 W x min(-1)), without the knowledge of ventilatory parameters, we recommend using the regression formula: H(TT)=0.84 x Hmax + 14.3 beats x min(-1) (r=0.85; p<0.001).