Participants in the sport of adventure racing often choose to go without sleep for a period of greater than 24 h while partaking in prolonged submaximal exercise. This study examined the effect of 30 h of sleep deprivation and intermittent physical exercise, on the cardiorespiratory markers of submaximal exercise in six subjects. Six subjects with the following physical characteristics participated in the study (mean +/- SD): age 22 +/- 0.3 years, height 180 +/- 5 cm, body mass: 77 +/- 5 kg, VO2peak 44 +/- 5 ml. kg (-1). min (-1). Three subjects engaged in normal sedentary activities while three others cycled on a cycle ergometer at 50 % VO2peak for 20 min out of every two hours during thirty hours of sleep deprivation. One week later sleep deprivation was repeated with a cross over of subjects. Every four hours, subjects completed assessments of cardiorespiratory function during 50 % VO2peak cycling. A 3 x 8 repeated measures ANOVA revealed a significantly lower heart rate with sleep deprivation (p < 0.05), but no other significant effects (p > 0.05) on respiratory gas exchange variables. Neither sleep deprivation, nor a combination of sleep deprivation and five hours of moderate intensity cycling, appear to be limiting factors to the physiological capacity to perform submaximal exercise.