An optimized automated IEF procedure in polyacrylamide micro gels and immunofixation with 10 monospecific antibodies against some fragments of the IgG molecule and against the whole IgG isotypes IgG(1), IgG(2), IgG(3), IgG(4), respectively, detected oligoclonal bands (OBs) within acid, neutral, and alkaline ranges of the gels. Accuracy and reliability of the OB assay for detection of an intrathecal IgG synthesis proved to be higher with immunofixation than with silver staining of bands precipitated by trichloroacetic acid. CSF OBs were specified as lambda or kappa IgG subfractions, respectively, duplex IgGs precipitated with anti-lambda, anti-kappa, and anti-Fc antibodies at the same pI. Most of OBs were classified as belonging to either IgG(1), IgG(2), IgG(3), or IgG(4) isotypes in CSF. The IEF procedure additionally allowed the discrimination of both free light chains and possible "free" heavy gamma chain fragments in CSF, when immunofixation was done with monospecific antibodies against both light chains and gamma chain fragments (e.g. anti-F(ab')(2), anti-Fd, anti-Fc, anti-C(H)2). The results pointed out a distinct heterogeneity of the IgG immune response in human CSF. The IEF procedure with extended immunofixation is recommended for completion of the basic laboratory procedures used in neuroimmunology in order to discriminate inflammatory processes in human CNS.