Soluble immune complexes prepared with reduced and alkylated antibodies persisted longer in the circulation than complexes prepared with intact antibodies, when these were administered intravenously to mice. The disappearance of complexes with reduced and alkylated antibodies was delayed in part because the initial phase of vascular permeability was considerably less than that seen following the administration of complexes with intact antibodies. In addition, large complexes with lattice structure of more than two antigen and two antibody molecules persisted longer in the circulation after administration of complexes with reduced and alkylated antibodies than after administration of complexes with intact antibodies. Thus, the concentration of large latticed complexes with reduced and alkylated antibodies was significantly greater than the concentrations of large latticed complexes with intact antobodies at all observed times through 96 hours. The persistence of large latticed complexes with reduced and alkylated antibodies was associated with significantly decreased hepatic localization of complexes with reduced and alkylated antibodies compared to the hepatic localization of complexes with intact antibodies at 1, 4, 12, and 24 hours. The observations indicated that the removal of large latticed complexes from the circulation by the hepatic mononuclear phagocyte system was decreased when reduced and alkylated antibodies were used for the preparation of immune complexes. The persistence of large latticed complexes with reduced and alkylated antibodies in the circulation was associated with enhanced and prolonged presence of glomerular deposits of immune complexes, as reported in the accompanying article (Haakenstad AO, Striker GE, Mannik M: Lab Invest 35:293, 1976.