Uptake of horseradish peroxidase (HRP) by sensory axon terminals was studied in lamellated corpuscles of mouse plantar foot pads after i.v. and local s.c. HRP injections. The corpuscles, considered to be rapidly adapting mechanoreceptors, are localized in dermal papillae and have discoid axon terminals enclosed in 1-5 lamellae of lamellar cells. The injected HRP diffused into interlamellar and adaxonal clefts and was taken up by sensory terminals, being incorporated in coated pits and coated vesicles formed by the axolemma. The tracer further appeared in the axoplasm in smooth vesicles, multivesicular bodies, and vacuoles. Similar incorporation of HRP into vesicles, inclusion bodies, and vacuoles was observed in the lamellae and perinuclear cytoplasm of lamellar cells. Vibratory stimulation considered to be adequate for this type of mechanoreceptors did not result in any perceptible increase in HRP uptake by sensory terminals. It is suggested that endocytosis by sensory terminals may serve for incorporation of regulatory macromolecules that presumably mediate information to the perikaryon about conditions of the distant terminals and their microenvironment.