A radioimmunoassay (RIA) was recently developed for the detection of antiviral IgG and IgM class-specific antibodies using antigen-coated polystyrene balls as the RIA solid-phase. In this communication the attachment and distribution of herpes simplex virus (HSV) capsid and envelope antigens and rubella viruses on the surface of the balls was examined by scanning electron microscopy (SEM). In SEM the surface of the untreated 'clear frosted' polystyrene balls appeared very uneven with innumerable pits and grooves. The viral particles were haphazardly distributed both in the grooves and on the exposed surface of the balls. The strength of adsorption of the viral antigens onto the balls seemed to be remarkably resistant to outside mechanical forces. HSV antigens frequently appeared in clusters, whereas rubella viruses were mostly found as single particles.