The immunocytochemical distribution of substance P in the guinea pig veatibular endorgans and the vestibular ganglion was investigated. Substance P like immunoreactivity was found in both ctistae of the semicircular canal and maculae in all specimen studied. By using electron microscopy, we confirm substance P like immunoreactivity is restricted within the primary afferent neuron. However, the immunoreactivity was not uniformly distributed throughout vestibular endorgans. More numerous reactive fibers were found in the slope of the cristae and in the peripheral region of the maculae.
