Chromatofocusing programs were designed for separations of submilligram amounts of normal and abnormal human IgG. The Pharmacia FPLC system, equipped with a Mono P column or a specially designed, small column was used for the separations. Normal IgG in paired cerebrospinal fluid and serum samples, paired samples from patients with intrathecal immunoglobulin G synthesis, as well as sera with IgG M components were examined. Abnormal immunoglobulin G components, especially those with pI values greater than ca. 7.0 pH units, were easily identified.