Stable hybridoma cell lines secreting monoclonal antibodies (MAb) to the yellow strain of cucumber mosaic virus (CMV-Y) were produced by fusing spleen cells of immunized BALB/c mice and mouse myeloma cell line P3-X63-Ag8-U1 (P3U1). Some of them were used to produce MAbs in ascitic fluid and their respective properties were characterized. Six out of seven MAbs in ascitic fluid reacted strongly with CMV-Y (Y serotype) and CMV-Z (P serotype). In contrast, one MAb reacted strongly with homologous strain and much more weakly with CMV-Z. The MAb which exhibits high activity and a wide spectrum of reactivity was conjugated to alkaline phosphatase. A comparison for the detection efficiency and sensitivity with MAb and rabbit polyclonal antibody (PAb) conjugates was made in DAS ELISA. The MAb conjugate could be used at higher dilutions (up to 8-fold) without loss of specific activity than that made with PAb. The efficiency and sensitivity for virus detection with MAb conjugate were superior to those with PAb. Also, DAS ELISA with MAb conjugate could detect efficiently heterologous serotype with higher ELISA values than those with PAb.