Perception of respiratory function may be an important factor in self-management of asthma. Previous research has suggested that asthmatics may not accurately perceive pulmonary functioning. The perception of normal and asthmatic individuals was assessed using a magnitude production procedure in a series of three studies, proceeding from normal individuals during rest, then submaximal exercise, to a comparison of normal and asthmatic adolescents during rest and submaximal exercise. At rest there were no differences between males and females, adults and adolescents, or asthmatics and non-asthmatics. However, there were significant differences in perception between rest and exercise for all groups. These findings suggest that a breakdown in perception does not occur during submaximal exercise in patients with asthma.