Studies of dorsal root ganglion (DRG) neurons are needed for the understanding of mechanisms underlying acute and chronic pain; these neurones are ideal targets for novel analgesics. Although mice are widely used for studies of DRG neurones in pharmacological research and drug development, published electrophysiological studies on DRG neurones in this species are all in vitro. In vivo intracellular recordings allow identification of neuronal properties, e.g. sensory receptive properties and conduction velocity, within the in vivo environment. This is important as the in vivo environment influences these neurones in many ways, and can be altered considerably in chronic pain states. We have therefore developed in vivo recordings in L4/L5 DRG neurones in adult mouse. Adult C57Bl6 male mice (26-35g) are deeply anaesthetized with initial sodium pentobarbitone (80-85mg/kg, i.p.) followed by regular further doses (25mg/kg, i.v.) to maintain deep anesthesia throughout. A tracheotomy allows for artificial ventilation as necessary and the left external jugular vein and carotid artery are cannulated to allow supplementary anaesthetic and blood pressure monitoring respectively. Following a laminectomy, the left L3-L6 DRGs are exposed and a pool constructed. Liquid paraffin maintained at 30°C is used to fill the pool, covering the tissues. Intracellular recordings with sharp glass microelectrodes filled with 3M KCl enable study of evoked somatic action potentials, conduction velocity measurement and identification of sensory receptive properties of DRG neurones as C, Aδ or Aα/β nociceptive neurones or as different types of low-threshold mechanoreceptive neurones. At the end of experiments, animals are killed with an anaesthetic overdose. Methods used to improve survival and recording stability will be demonstrated. Preliminary analysis of electrophysiological properties shows that the distinct patterns of somatic action potential configuration in relation to sensory properties are similar in these C57Bl6 mice to those previously reported in rats and guinea pigs.