Acid-sensing ion channels (ASICs) are cation-permeable membrane proteins activated by extracellular protons that belong to the degenerin/epithelial sodium channel superfamily. ASICs are highly expressed in the mammalian peripheral and central nervous tissue. ASIC1a is predominantly expressed in neurons of the CNS. Its splice variant ASIC1b, however, is almost exclusively localized in peripheral sensory neurons. Sensory neurons of the dorsal root ganglia (DRG) express ASIC1a, ASIC1b, ASIC3, and ASIC2b. In the peripheral nervous system ASICs contribute to nociception during inflammation and tissue acidosis. The fact that ASIC1b can be found only in a subset of small and large diameter DRG neurons, as shown by in situ hybridization, indicates a specialized function in sensory transmission. The exact function of ASIC1b is to date unclear. We used whole-cell patch-clamp to characterize the proton-activated currents in cultured mouse DRG neurons. As previously reported, acidification to pH6.5- pH5 elicits transient or sustained currents in these neurons. According to their proton affinity and activation/inactivation kinetics, we classified the neurons in 4 classes. 12% of all neurons were not responsive to acidification. 39% showed a sustained current to pH6 and below. Within the population of proton-responsive neurons with a transient response, 15% reached the maximal activation at pH6 and 34% at pH5. 13% out of the 2^nd population showed inactivation characteristics corresponding to ASIC1b. We are on the way to confirm the electrophysiogical data by immunofluorescence of DRG cryo slices. Based on our results we conclude that ASIC1b is expressed in 13% of medium-large sized DRG neurons.