The purpose of this study was to examine the relative importance of physiological characteristics during firefighting performance, as assessed by the Candidate Physical Ability Test (CPAT). Participants included professional and volunteer firefighters, ages 18-39 (n=33). Muscle strength, muscle endurance, muscle power, body composition, aerobic capacity, anaerobic fitness, and the cardiovascular response to stairclimbing were assessed to determine the physiological characteristics of the participants. To quantify firefighting performance, the CPAT was administered by members of the fire service. Absolute and relative mean power during Wingate anaerobic cycling test (WAnT), relative peak power during WAnT, and absolute maximal oxygen uptake (VO₂max) were significantly higher in those who passed the CPAT (n=18), compared to those who failed (n=15) (P < 0.01). Absolute and relative mean power during WAnT, fatigue index during WAnT, absolute VO₂max, upper body strength, and the heart rate response to stairclimbing were all significantly related to CPAT performance time (all P < 0.01). However, absolute VO2max and anaerobic fatigue resistance during WAnT combined were the best predictors of total CPAT performance (Adj. R² = 0.817; P < 0.001). Performance on the ceiling breach and pull was the only individual CPAT task that could not be significantly predicted by the physiological characteristics assessed. Rate-pressure product during the stairclimb was not related to CPAT performance. In conclusion, measures of anaerobic and aerobic fitness best predict overall CPAT performance, as well as individual task performance. Remedial programs aimed at improving firefighting performance should target anaerobic and aerobic fitness qualities.