Light microscopic immunoenzymatic and immunofluorescence histochemistry revealed co-existence of opioid peptides with substance P in primary sensory neurons of all segmental dorsal root and trigeminal ganglia of guinea-pig. Sensory opioid peptides appeared to be exclusively processed from prodynorphin and include [Leu]enkephalin, neoendorphins, and dynorphin A. We suggest the presence of presynaptic opioid autoreceptors in primary sensory afferences.