The IgG subclass distribution for both ANCA-specific, and total IgG subclasses, of sera from 48 patients with active systemic vasculitis was determined by solid-phase assay using monoclonal anti-human subclass reagents. To control for varying performance of the subclass reagents, the assays were calibrated with sera affinity-depleted into subclass specific fractions, whose ANCA IgG subclass distribution was determined by a common reagent. In 10 patients whose ANCA persisted during clinical remission, the ANCA IgG subclass distributions between active and remission phases of disease were compared. The total IgG subclass distribution of sera from patients with active vasculitis was similar to that found in a normal population. The ANCA IgG subclass distribution of the same sera showed relative enrichment for IgG3 and depletion of IgG2 (P less than 0.05). When the active and clinical remission ANCA IgG subclass distributions were compared, ANCA IgG3 levels had fallen and ANCA IgG2 levels were increased during remission (P less than 0.01).