Interleukin-17A (IL-17A) is a proinflammatory cytokine which is important in autoimmune diseases such as rheumatoid arthritis. Recently we found that IL-17A is also pronociceptive. A large proportion of dorsal root ganglion (DRG) cells express IL-17A receptors, and application of IL-17A into the rat knee joint sensitized nociceptive joint afferents to mechanical stimuli. Interestingly, however, a low concentration of IL-17A reduced the responses of Aδ fibers to mechanical stimulation. In order to further explore the role of IL-17A in nociception we studied here the effect of IL-17A on Na⁺ currents in small- to medium-sized mouse DRG neurons using patch-clamp recordings. We used either WT mice, Na_v1.8 or Na_v1.9 knockout mice. IL-17A was applied to the bath at doses of 10 and 100 ng/ml, and we tested its effect on the magnitude of different types of Na⁺ currents. In part of the experiments we administered TTX 500 nM to the bath. After bath application of 100 ng/ml IL-17A, WT mice exhibited an increase of TTX resistant Na⁺ currents of about 25%. In Na_v1.9^-/- mice TTX resistant Na⁺ currents increased by about 30%. In Na_v1.8^-/- mice, without TTX, we found a reduction of Na⁺ currents by 70%. After bath application of 10 ng/ml IL-17A, the increase of Na⁺ currents was between 5% and 10%, whereas the reduction of TTX sensitive currents was about 50%. From these experiments we conclude that IL-17A increases TTX resistant Na⁺ currents but rather decreases TTX sensitive Na⁺ currents. These findings may explain the response pattern described above.