The substantia gelatinosa (SG) (LII) is a region of the dorsal horn of the spinal cord that receives high densities of unmyelinated primary "C-fibres" of cutaneous origin. These "C-fibres" bind IB4, which is a useful marker for the "non-peptidergic" group of primary afferents. Studies using tracers to retrogradely label dorsal root ganglion (DRG) neurons that bind IB4 suggest that many of these fibres project to the skin. Unfortunately, due to the binding of IB4 to the epidermal layer, it is not possible to evaluate in detail the finer structure of their terminals. Transgenic mice were produced in which the Thy1.2 promoter drives the expression of enhanced green fluorescent protein (eGFP). In these mice, eGFP was found in primary afferent fibres innervating the epidermis and hair follicles in hairy skin. No eGFP-containing afferents were found in non-hairy skin, or other tissues or organs. In the DRGs, most of the eGFP fibres stainined positively for IB4, but did not colocalise substance P or CGRP. In the spinal cord, these eGFP primary afferents targeted the SG. Patch-clamp recording from SG neurons receiving afferent input from the eGFP epidermal afferents suggests that they contain TRPV1, and pre-and post-synaptic m-opioid receptors, and have the morphology of "stalked cells". These observations suggest that LII is concerned with the processing of sensory information, such as thermal and chemical sensation, from the epidermis.