The voltage-gated K+ channel Kv3.1 is expressed in skeletal muscle and in GABAergic interneurons in the central nervous system. Hence, the absence of Kv3.1 K+ channels may lead to a phenotype of myogenic or neurogenic origin, or both. Kv3.1-deficient (Kv3.1-/-) 129/Sv mice display altered contractile properties of their skeletal muscles and show poor performance on a rotating rod. In contrast, Kv3.1-/- mice on the (129/Sv x C57BL/6)F1 background display normal muscle properties and perform like wild-type mice. The correlation of poor performance on the rotating rod with altered muscle properties supports the notion that the skeletal muscle dysfunction in Kv3.1-/- 129/Sv mice may be responsible for the impaired motor skills on the rotating rod. Surprisingly, we did not find major differences between wild-type and Kv3.1-/- 129/Sv skeletal muscles in either the resting or action potential, the delayed-rectifier potassium conductance (gK) or the distribution of fast and slow muscle fibers. These findings suggest that the Kv3.1 K+ channel may not play a major role in the intrinsic excitability of skeletal muscle fibers although its absence leads to slower contraction and relaxation and to smaller forces in muscles of 129/Sv Kv3.1-/- mice.