A method for the preparation of model immune complexes of heat-aggregated human IgG with predetermined molecular masses is described. IgG complexes with different molecular masses were produced by incubation of human IgG for 20 min at 63 degrees C, the protein concentration varying from 0.5 to 5 mg/ml before heat treatment. To determine the bulk of IgG molecules included in the aggregates, the IgG complexes obtained were precipitated by 7% polyethylene glycol. The relative molecular masses of the heat-aggregated IgG preparations were calculated using light-scattering measurements, being expressed as the number of IgG molecules per aggregate (MIC/MIgG). The dependence of the MIC/MIgG value upon IgG concentration in aggregation was plotted. This dependence makes it possible to produce IgG model immune complexes with pre-determined molecular masses.