Gender differences in lung volumes and flow rates, and in respiratory control have been documented previously. How these gender differences affect exercise responses in normal subjects is less clear, particularly as many studies involved highly fit subjects. This study aimed to investigate potential gender differences occurring during progressive exercise in healthy males and females of average fitness. Fourteen males and ten females of mean (SD) age 23 (0.35) years completed a progressive exercise test to exhaustion on a cycle ergometer, with a ramp increase of 15 W min(-1) (female) or 20 W min(-1) (male). All females were studied during the follicular phase of their menstrual cycle. Cardiorespiratory variables were measured, breath by breath, and values were compared at rest, at 40 W, at physiologically equivalent workloads below, at and above the gas exchange threshold and at peak oxygen uptake (VO(2peak)). Mean VO(2peak) (SEM) was 32.4 (2.01) ml kg(-1) min(-1) for the females and 41.9 (1.80) ml kg(-1) min(-1) for the males. Females had a significantly lower end-tidal partial CO(2) pressure at rest and throughout exercise. Increases in exercise minute ventilation were achieved by a significantly greater tidal volume in males, whereas females adopted a significantly greater breathing frequency. Ratings of respiratory discomfort were significantly greater in the male group at physiologically equivalent workloads compared to the female group. This study shows gender differences exist in the ventilatory and sensory response to progressive exercise in untrained subjects. Further work is required to ascertain if these effects are altered during the luteal phase of the menstrual cycle.