To develop an enzyme immunoassay (EIA) for IgM antibody to hepatitis E virus (HEV) (IgM anti-HEV) and IgG antibody to HEV (IgG anti-HEV), a synthetic gene encoding several liner immunodominant antigenic epitopes from HEV structural proteins was assembled as a chimeric recombinant mosaic protein (Mpr) with glutathione S-transferase and used as an immunodiagnostic target. In addition, a neutralization confirmation test was developed using individual synthetic peptides. Among 614 patients with acute hepatitis from 10 geographically distinct outbreaks, IgG anti-HEV was found in 546 (88.9%), with a range of 77-100% depending on the outbreak. Of 130 patients tested for IgM anti-HEV, 126 (96.9%) were positive. Among patients tested within 4 months of onset of jaundice, 37/37 (100%) were IgG anti-HEV positive. For patients from whom sera were collected 1-16 days after onset of jaundice, the geometric mean IgG titer (GMT) was 1:47,000; the GMT increased to 1:70,710 30-40 days after onset of jaundice and decreased to 1:1,778 3-4 months after the onset of jaundice. For patients tested 6-8 months after onset of jaundice, 11/12 (92%) were IgG anti-HEV positive, and the GMT was 1:2,908. IgM anti-HEV was detected in 43/43 (100%) sera collected 1-40 days after onset of jaundice, and the GMT for IgM anti-HEV was 1:10,000 at that time. For sera collected 3-4 and 6-12 months after onset of jaundice, 7/14 (50%) and 5/12 (40%) respectively, were IgM anti-HEV positive. In conclusion, an artificial mosaic protein composed of linear antigenic epitopes from open reading frame 2 (ORF2) and ORF3 of HEV has been successfully applied to the development of a sensitive and specific EIA for the detection of IgG and IgM anti-HEV activity. These assays were used for the verification of HEV infection in outbreak settings and for the diagnosis of HEV infection in sporadic cases.