We previously reported that hepatocyte growth factor (HGF) had a stimulatory effect on hair growth in vivo and in vitro. The secreted inactive form of HGF is processed into an active form by serine proteinases such as HGF activator and urokinase. The mRNA expressions of various proteinases and their inhibitors in relation to HGF activation in hair growth were examined using animals with a synchronous hair cycle. Total RNA were extracted from the anterior dorsal skin of rats in different hair cycle stages, and mRNA expressions of the specific genes were compared using semiquantitative reverse transcription polymerase chain reaction. The mRNA of HGF, HGF activator, urokinase, plasminogen activator inhibitor (PAI)-1, nexin-1, matrix metalloproteinase (MMP)-2, and tissue inhibitor of metalloproteinase (TIMP)-1 were expressed strongly in anagen tissue and slightly in telogen tissue. Moreover, topical application of 1% minoxidil sulfate to the anterior dorsal skin of rats in telogen stimulated hair growth and increased the mRNA expressions of HGF and MMP-2. These findings suggest that some proteinases and their inhibitors, strongly expressed in anagen, may act as hair growth regulatory molecules, and may also be involved in processing the latent form of HGF.