Damage to motor neurons induces regeneration processes including axonal growth and change of synaptic properties. Sensory axons that run along the motor axons are also damaged, but their possible role in the motor neuron's regeneration is generally ignored. Here, the effect of eliminating some sensory inputs from intact motor axons on the motor axon's properties was studied. Micro–dissecting one of the segmental, bilateral, sensory stretch receptor pairs of the crayfish abdomen induced the deep extensor abdominal motor axons to grow and changed their synaptic properties. The results demonstrate directly, probably for the first time, that change in sensory neuron activity can induce motor axons to grow, form new synapses, and change their synaptic properties.