The results of the present study, in the rat and cat, indicate that not only a lesion of peripheral nerve or capsaicin pretreatment but also pharmacological deafferentation with local anaesthetic or disruption of the connections between primary sensory neurons and the central nervous system are effective in producing dystrophic changes in tissues. These effects of deafferentation do not seem to depend on the sympathetic or parasympathetic efferents. Dystrophic changes are connected with microcirculation disturbances: slow down of local blood flow, elevation of the vascular permeability, oedema and leucocyte infiltration. The findings indicate that capsaicin-sensitive primary sensory neurons are the afferent part of some reflex arrangement which participates in the regulation of microcirculation and the maintenance of trophic processes in peripheral tissues. The efferent part of this arrangement is unknown.