A seroepidemiological study of rotavirus was conducted in the northern part of Tokyo from 1990 to 1992 by using reverse transcription-polymerase chain reaction (RT-PCR). G1 and G3 types were detected in the winter between 1990 and 1991, however G1 type was appeared mainly in the winter between 1991 and 1992. G3 type was observed as the main type during the winter in the 10 year survey in the Tokyo area for the first time. RT-PCR was useful in the seroepidemiological studies of rotavirus infection.