Using combined immunohistochemical and receptor binding techniques, substance P-containing sensory neurones of rhesus monkey cervical dorsal root ganglia were examined for the presence of opiate or histamine (H1) receptors. Serial sets of three sections were examined sequentially for substance P-containing neurones, opiate receptors using [3H]etorphine binding and histamine (H1) receptors using [3H]mepyramine binding. Of 3484 dorsal root ganglion cells, 513 contained substance P. Of 30 randomly chosen substance P-positive neurones, 6 possessed opiate receptors and 7 histamine receptors, including 4 neurones with both sets of binding sites. The results are interpreted to suggest that both nociceptors and non-nociceptive sensory inputs may be biochemically heterogeneous and that a simple correlation between substance P content and a particular receptive field profile is unlikely.