Due to their great content in neuraminic acid and/or nucleic acids, most of the circulating immune complexes run significantly faster as unbound gammaglobulins during agar gel electrophorsis. Because of their Ig components they can be easily detected in the alpha-1, inter-alpha, alpha-2 and beta fractions of human sera with monospecific anti-Ig-sera by counterimmunoelectrophoresis. The presence of complement component 3 and of fibrinogen, in some cryoglobulinemias can be demonstrated in the same way. Nucleic acid content (both RNA and DNA), and presence of neuraminic acid in precipitated immune complexes can be demonstrated by usual histologic methods (Giemsa, methyl green-pyronine, PAS [periodic acid-Schiff] or Aminoff) on washed and dried slides.