The effects of rhythmic input on breath period (TT) under constant metabolic drive were assessed in 10 musically trained and 10 untrained subjects. They tapped to a metronome and then to four musical segments, each for 5 min. Ten of these subjects (5 from each group) also listened to the selections without tapping. TT, beat period (TB), and phase coupling (PC) were assessed during the last 20 breaths of each presentation. TT coefficient of variation decreased significantly (P less than 0.001) in all subjects (base line = 23%; listening = 15%; listening and tapping = 10%). Significant correlation between rhythm and TT, indicating relative entrainment, was found in half of the subjects (r greater than 0.45; P less than 0.01). Significant integer TT/TB ratio and PC, both indicating tight entrainment between rhythm and breathing, were observed in 12 subjects (though not consistently in each one). These data advance the following hypothesis: musical rhythm can be a zeitgeber (i.e., pacemaker), with its ability to entrain respiration dependent on the strength of its signal relative to spurious signals from the higher neural centers that introduce noise into the central pattern generator. Tapping reinforces the zeitgeber, increasing its signal-to-noise ratio and thereby promoting entrainment.