Serum samples collected periodically from a 40-year-old Japanese woman who had not travelled abroad and who had contracted sporadic acute hepatitis E in 1993 were semi-quantitatively tested by enzyme immunoassay for IgM, IgA and IgG antibodies to hepatitis E virus (HEV). Anti-HEV IgM and IgA antibody levels were the highest (1 : 2400 dilution and 1 : 3400 dilution, respectively) on day 9 after the onset of hepatitis and then decreased rapidly in a parallel manner. Anti-HEV IgG antibody levels were the highest (1 : 17000 dilution) on day 145 and then decreased gradually but remained at high titres (1 : 2200 dilution) even 8.7 years after the onset of hepatitis. An HEV isolate, HE-JA10, recovered from the patient's serum at admission was closely related to a genotype III strain isolated in the United States (US1), with 92.2% identity over the full-length genome, and was most closely related to the JMY-Haw isolate of Japanese origin (95.4% identity).