Mice are the most widely used experimental mammals, and many inbred strains are available. However, except for the relatively recent strains derived from known wild populations, the relationships between wild and laboratory mice are not well understood. Based on the Y-chromosomal restriction fragmentlength polymorphism, seventeen inbred strains were classified into two groups: strains with the Mus musculus musculus type Y chromosome and those with the M. m. domesticus type Y chromosome. We extended the survey to an additional twenty-two inbred strains. The M. m. musculus type Y chromosome was found in AEJ/GnLe, AAU/SsJ, BDP/J, BXSB/MpJ, DA/HuSn, HTG/GoSfSn, I/LnJ, LP/J, NZW/LacJ, RIIIS/J, SB/Le, SEA/GnJ, SF/CamEi, SK/CamEi, SM/J, WB/ReJ, WC/ReJ and YBR/Ei, while the M. m. domesticus type Y chromosome was present in BUB/BnJ, MA/MyJ, PL/J and ST/bJ.