Several geographically and biologically distinct isolates of peanut stripe Potyvirus (PStV) were tested against available polyclonal and monoclonal antibodies. In direct antigen-coated, enzyme-linked immunosorbent assay (DAC-ELISA), the polyclonal antisera prepared against the purified virus reacted with all the isolates tested. However, a monoclonal antibody, 3AB5, also prepared against the purified virus showed dramatic difference in its reactivity to the same isolates. Tested against blotch isolates from Georgia, Virginia, and Florida, 3AB5 reacted with two of 10 isolates. The reaction was either strongly positive or negative. Antibody 3AB5 did not react with a necrotic strain of PStV from Taiwan. Results indicate the existence of antigenic diversity among PStV isolates.