A new method has been developed to label primary afferent fibers in the vestibular nerve with the use of extracellularly applied horseradish peroxidase(HRP) in the inner ear space. Only the fibers innervating organs whose sensory receptor areas are mechanically damaged take up and transport HRP onto the brain stem. In 32 chinchillas, vestibular nerve labelling was performed successfully in all animals by scratching the surface with an electrolytically sharpened needle and replacing the fluid in the vestibule with 30% HRP solution. The animals were incubated for 48 hours prior to Diaminobenzidine(DAB) processing. This was found to be the optimal time for labelling the fibers projecting into the vestibular nuclei. Only fibers innervating the damaged receptors were labelled. Simply replacing the vestibular fluid with HRP did not label the ganglion cells nor the afferent fibers in the brain stem. The specificity of the labelling was verified by histological inspection of the ganglion cells and nerve fibres innervating the damaged and intact receptors.