Shell morphology and length of the nonrepetitive region of the foot protein 1 (adhesive protein) amplified by the polymerase chain reaction (PCR) using oligonucleotide primers, Me 15 and Me 16, were examined in mussels collected from Asamushi water, northern Japan, and compared to those of M. galloprovincialis Lamarck from Maruishi, Hiroshima, Japan. The Asamushi mussels were collected from a suspended rope substrate and M. galloprovincialis of Maruishi from a floating dock. The mussels of the Asamushi area have been referred to as M. edulis Linnaeus or M. edulis galloprovincialis Lamarck, and were recently supposed to be M. galloprovincialis and/or M. trossulus Gould based on the geographical distributions of these species. Although 14 of 19 variables of shell characters differed significantly between mussels of Asamushi and M. galloprovincialis from Maruishi, both canonical variates analysis using eighteen shell characters and PCR product analysis showed that the mussels from Asamushi were M. galloprovincialis. The result of PCR product analysis also indicated no hybridization between M. galloprovincialis and M. trossulus in the Asamushi area.