A simple and rapid spot test for visual immunoassay based on latex immunoturbidimetry has been developed. A cationic dye, Ethyl Violet, was used as a labeling agent to bind to bovine serum albumin on latex particle surface. When a 10 mu L sample solution is set on a hydrophilic polytetrafluoroethylene membrane film, a blue ring-shaped stain is formed on the film surface. This method has been successfully applied to C-reactive protein.