Arm and leg movements are known to produce temporal pattern changes of breathing. This can be interpreted as coordination, as defined by von Holst (1939). The aim of the present study was to find whether breathing exerts an influence in a reverse direction on a nonrespiratory movement as well. A pursuit tracking test was used, and test individuals (N = 19) were instructed to track a visually presented step function by flexion or extension of their right index finger. Velocity and precision of the step responses proved to be dependent on their relation to the breathing time course; the differences between inspiratory and expiratory responses were smaller than those within each half-cycle. The movements were performed more rapidly and more precisely in about the middle of each half-cycle than immediately after the respiratory phase transition or during the second half of each inspiration or expiration. Discontinuous short-lasting motor actions exerted a coordinative influence on respiration comparablewith that of periodical events: Breaths coinciding with step responses were shortened, preferably when the preset step was given early in the inspiration. It was hypothesized that the reciprocal effect between both motor actions changes periodically. In the first part of each respiratory half-cycle, the respiratory rhythm exerts only a weak influence on additional movements, but it can be altered easily by simultaneous motor processes. Toward the respiratory phase-switching, the respiratory rhythm behaves more stably against coordinative influences and becomes capable of impairing an additional movement.