A rapid quantitative determination of low concentrations of IgG using 125I labelled protein A

125I labelled protein A was used to develop a solid phase radioassay for the determination of low concentrations of immunoglobulins G in serum, cerebrospinal fluid, and lymphocyte culture supernatants. This radio-assay is sensitive (200 ng/ml), rapid, technically simple and economical. There is no significant cross reaction with IgA and IgM. The assay does not require any specific reagents and gives a good correlation with radial immunodiffusion test (serum: r = 0,83; CSF: r = 0,913).