1. Efferent nerve fibres innervating the lateral-line sense organs of the dogfish Scyliorhinus were stimulated with trains of stimuli while spontaneous afferent activity was monitored.
2. Significant changes in spontaneous impulse frequency could be produced when the efferent nerves were stimulated by trains of pulses at frequencies between 20-100 sec-1 lower stimulus frequencies had no visible effect. The impulse frequency decreased or was totally inhibited during the stimulus period and for 150-200 msec following it. The inhibitory effect was very variable and declined with repetitive stimulation.
3. Stimulation of the efferent nerves to inactive afferent units was followed after 500 msec by a brief low-frequency discharge.