Radioimmunoassay procedures of sufficient sensitivity (IgG, 0.5 mug per 100 mul; IgA, 25.0 ng. per 100 mul; IgM, 10.0 ng. per 100 mul; IgD, 0.5 U. per 100 mul; and IgE, 1.0 U. per 100 mul) were developed detect and quantitate all 5 immunoglobulin classes in the cerebrospinal fluid on small aliquots (1 ml.) of unconcentrated cerebrospinal fluid. All 5 immunoglobulin classes were routinely detected in normal individuals for the first time, the levels varying with different age groups for IgG and A but not for the remaining immunoglobulin classes. Race and sex had no effect. Standardization of techniques and establishment of normal values for different age groups sets the stage for determination of immunoglobulin changes related to central nervous system disease.