The ventilatory effects of biceps tendon vibration were studied in healthy human subjects at rest and at two levels of light leg exercise. This was performed with intent to add the ventilatory effects of selective stimulation of muscle spindles to nervous and humoral respiratory inputs from contracting muscles. Tendon vibration performed in individuals at rest elicited a marked increase in respiratory frequency and in the ratio between inspiratory time and total breath duration with variable changes in tidal volume; this was in agreement with previous results (Jammes et al., 1981). When stimulation of biceps proprioceptors was performed during steady state exercise, the changes in ventilatory timing were attenuated, but variations in tidal volume often occurred. These results suggest that, when respiratory centers are being entrained by performance of work, further activation of muscle receptors exerts complex effects on the breathing pattern with a lack of facilitatory influences in ventilation and gas exchange.