By means of reverse transcription-polymerase chain reaction using various pairs of primers, 902 strains of Norwalk-like viruses (NLVs) were detected during 10 years from 1989 to 1998 in the nationwide area of Japan including Hokkaido and Okinawa. Nucleotide sequencing was done on 177 strains, and we found that 153 strains (86%) of them belonged to geno-group II (GII). GII could be classified into five subgroups (G2A, G2B, G2C, G2D and G2E) based on the amino acid sequences showing a similarity of more than 91%. Among them G2C and G2D (named JP1) as well as G2E (named JP2), which were occasionally identified in Japan (detection rate of 17%) but rarely detected in the other countries, revealed to form new subgroups. From the above analysis, three pairs of new primers were established as consensus primers for NLVs. All the three sets of primers, P1/P2,P1/P3 and Y1/Y2, amplified both GI and GII equally and efficiently.