An enzyme linked immunosorbent assay (ELISA) for detection of antibodies to mammalian cell-expressed E2 protein of GB virus C (GBV-C E2) is described. Antibodies to GBV-C E2 are captured on a solid phase coated with affinity purified E2 protein. Bound antibody is detected in an indirect assay format using horseradish peroxidase (HRPO) labeled goat anti-human IgG as the secondary antibody. Following a color development step, absorbance at 492 nm is measured. A population of 100 volunteer blood donors was tested to assess the specificity of this assay. Individuals reactive for antibody to GBV-C E2 can be considered to have been exposed to GB virus C.