The question whether aquaporin 3 (AQP3) is expressed in normal human skeletal muscle at mRNA and protein levels has been examined, since AQP3 has been reported to be coexpressed with AQP4 in various kinds of tissues other than skeletal muscle. The gel electrophoresis of the reverse transcription polymerase chain reaction (RT-PCR) product of total RNA samples extracted from normal human muscle specimens by using the oligonucleotide primers for AQP3 contained a band of 629 base pairs which corresponded to the base pair length between two primers of AQP3. The nucleotide sequence of this RT-PCR product coincided with that of AQP3. At the protein level, immunoblot, immunohistochemical and immunoelectron microscopical studies were done by using rabbit antibody against the synthetic peptide of the cytoplasmic domain of the human AQP3 molecule. Immunoblot analysis showed that rabbit antibody against the human AQP3 reacted with a protein of approximately 30 kDa molecular weight in extracts of normal human skeletal muscles. The immunoreaction for the anti-AQP3 antibody with normal human muscle was noted at the myofibre surface. Immunogold labelling electron microscopy revealed that the gold particles indicating the presence of AQP3 molecules were located mainly at the inside surface of muscle plasma membrane.