Serotypes and RNA electropherotypes of group A human rotaviruses were identified in stool samples from patients with acute gastroenteritis in Kasukabe Kosei Hospital, Saitama, Japan, during three rotavirus seasons from 1988 to 1991. Of the 665 stool samples from patients with acute gastroenteritis, 169 (25.4%) stool samples were positive for group A human rotaviruses. Of these 169 samples, 98 (58.0%) were serotype 1, 7 (4.1%) serotype 2, 14 (8.3%) serotype 3, 3 (1.8%) serotype 4 and 47 (27.8%) were untypable. Serotype 1 was predominant over all three rotavirus seasons. Serotype 2 was most prevalent in the second rotavirus season, serotype 3 in the third season. Serotype 4 was detected only the second rotavirus season. The ratio of subtype I to subtype II was 4.5:95.5. Among the 162 strains examined, 139 specimens were available to be electropherotyped. Fifteen different RNA electropherotypes were detected. Three to four different electropherotypes were more prevalent in each rotavirus season and the detection rate in each year was different within the same electropherotypes. The rotavirus strains of the same electropherotypes were observed with high prevalence for every rotavirus seasons. The same electropherotypes was found in human rotavirus strains of different serotypes that were appeared at different epidemic seasons.