PURPOSE: The steep ramp test (SRT) can be used to provide an indication of exercise capacity when gas-exchange measurements are not possible. This study evaluated the clinical usefulness of the SRT in adolescents with cystic fibrosis (CF) and compared the physiological responses of the SRT with the standard cardiopulmonary exercise test (CPET). METHODS: Forty CF patients (17 boys and 23 girls, mean +/- SD age: 14.7 +/- 1.7 years, FEV1: 86 +/- 18% of predicted) performed a SRT and a CPET with respiratory gas analysis in a randomized balanced design. Peak work rate (WRpeak), heart rate (HRpeak), minute ventilation (VEpeak), and oxygen uptake (VO2peak) were the main outcome measures. RESULTS: CF patients attained values for absolute and relative WRpeak during the SRT of 82 +/- 14% and 92 +/- 14% of predicted. Nutritional status and degree of airway obstruction did not influence SRT performance. Significantly higher values were attained for WRpeak during the SRT compared to the CPET (252 +/- 60 vs. 174 +/- 46 W; P<0.001), while significantly lower values were achieved for HRpeak (168 +/- 14 vs. 182 +/- 12 beats.min; P<0.001), VEpeak (59.2 +/- 19.5 vs. 72.0 +/- 20.2 L.min; P=0.006), and VO2peak (36.9 +/- 7.5 vs. 41.5 +/- 7.6 mL.kg.min; P=0.008). A strong correlation between WRpeak attained at the SRT and the VO2peak achieved during the CPET was found (r=0.822; P<0.001). CONCLUSION: The SRT seems to be a quick, convenient, and low-cost exercise test that is well-tolerated in patients with CF with mild-to-moderate airway obstruction. It provides an indication of exercise capacity and can potentially be used when exercise testing using gas-exchange measurements is not possible.