Peptide histidine methionine-like immunoreactivity (PHM-IR) has been demonstrated to be present in the human penis both by radioimmunoassay and immunohistochemistry with particularly high levels in the corpus cavernosum and vas deferens. In the cavernosa, PHM-IR has been localised entirely, in nerves around arteries. High performance liquid chromatography indicated that this PHM-IR co-eluted with synthetic PHM but not porcine PHI. The presence of PHM-IR in the penis suggests that this neuropeptide may play a functional role in penile function.