Potassium (K+) channels are believed to regulate mammalian sperm acquisition of fertilising capacity. However, the molecular identity of these proteins in sperm has not been elucidated. In this report, using immunoconfocal and electron microscopy we show that a minimum of four different classes of K+ channels (Kv1.1, Kv1.2, Kv3.1 and GIRK1) are present and regionally distributed over the surface of mouse epididymal sperm. In addition, the use of reverse transcription polymerase chain reaction on RNA from mouse spermatogenic cells allowed the amplification of multiple transcripts corresponding to the channels identified by immunocytochemistry. Consistent with this, whole-cell patch-clamp recordings showed the expression of at least two different outwardly rectifying K+ currents in spermatogenic cells.