Substance P immunoreactive elements were detected in the nervous system of the earthworm, Lumbricus terrestris using peroxidase-antiperoxidase method. Each part of the central nervous system contains immunoreactive perikarya. The central neuropil shows no stained fibers. Immunopositive nerve cells were found in the stomatogastric ganglia as well as nerve cells and fibers in the wall of the alimentary canal. In the body wall, epidermal sensory cells and fibers surrounding the chaetae display immunoreactivity. The results are compared with those described previously by other authors.