Six monoclonal antibodies (MoAbs) against potato virus A (PVA) were prepared and used in enzyme-linked immunosorbent assay (ELISA), immunoblot analysis and electron microscopic study of the virus. Four MoAbs, 151, 290, 328 and 634, reacted with purified virus preparation in dot blot test and showed strong reaction also with virus coat protein (CP) denatured by sodium dodecyl sulphate (SDS), while two MoAbs, 534 and 187, gave significantly weaker reaction with denatured CP than with purified virus. On electron micrographs, MoAb 534 effected binding only on few separate locations of the virus surface after prolonged storage. We presume that this MoAb recognized a conformation-dependent epitope.