A simple test using latex-agglutination was developed to detect serologically tobacco mosaic virus (TMV), soybean mosaic virus (SoyMV), and barley stripe mosaic virus (BSMV) from infected Plants. Latex spheres ( 0.81 $mu$, Difco) were adsorbed with immuno globulin purified by electrophoresis from crude antiserum against viruses. The antibody- sensitized latex suspension was mixed with sap from virus -infected leaves in a glass capillary tube (inner diam. 1mm $ imes$ 100 mm length) The mixture, after agitation, was observed under a stereo microscope at low magnification (X20 - X4O), to examine the reaction between antigen (Virus) and its antibody. Flocculation occurred when the reaction was positive.