Nucleotide sequences for the VP7 gene of human group C rotavirus were determined for two strains isolated in Okayama, Japan, during a 1988-1990 epidemic. These isolates, OK118 and OK450, were selected as prototypes of two different electropherotypes, patterns I and II, respectively. The genes were identical in size (1,063 bp), and both contained singled open reading frames encoding 332 amino acids. The alignment of two sequences revealed 46 nucleotide substitutions, 11 of which were predicted to give amino acid changes. The deduced amino acid sequence of VP7 from OK118 was similar to published sequences of a Japanese isolate and three foreign isolates (more than 98.4% identity), whereas the VP7 sequence of OK450 revealed around 96% identity with these isolates and had nine unique amino acid substitutions. The VP7 genes of nine Okayama isolated were than analyzed by dot blot hybridization with the VP7 probes of OK118 and OK450. Under highly stringent conditions, the OK118 probe produced strong hybridization signals with the genes of five pattern I strains and one pattern II strain, while the OK450 probe strongly reacted only with those of three pattern II strains. Our results concluded that relative sequence diversity in the VP7 gene was observed between two different electropherotypes prevalent in a limited area.