The improvement of instruments and technology enabled the first visualization of viral particles by means of electron microscopy in 1939 (1 ). In particular, the negative staining technique provided high-resolution electron microscopic images of viral particles This technique utilizes the principle of surrounding viral particles with electron-dense heavy metal atoms, whereby viral particles are recognized as negative contrast against a dark background of heavy metal atoms. The disadvantage of the so-called negative staining technique is that only small amounts of the sample are examined. Therefore, a highly concentrated virus suspension is usually required in order to visualize the viral particles. Since electron microscopic detection of virus in general requires particle concentrations in the range of 109 –1012 particles/mL (2 ), and most clinical specimens contain a concentration of viral particles much less than this range, additional procedures are required to increase the concentration of viral particles before visualization. The addition of specific antibody to the specimen may produce antigen-antibody aggregates and enhance viral concentrations within the immune complex, thereby facilitating electron microscopic detection. This immunoelectron microscopic procedure improves the sensitivity of electron microscopy by approx 1000-fold, and offers the advantage of identifying the immunologic specificity of the viruses (3 ).