As reported previously, gamma interferon (IFN-gamma) production was selectively decreased in thermally injured mice (TI-Mice) and spleen cell cultures from the mice following stimulation with various IFN inducers. The decrease in IFN production was associated with splenic suppressor macrophages. The present study demonstrated that TI-Mice treated with Ge-132 (TGe-Mice) produced IFN following stimulation with IFN-gamma inducers. The level of IFN activity detected in the sera of TGe-Mice approximated that of controls. Similar results were obtained when spleen cells prepared from TGe-Mice were stimulated with IFN-gamma inducers in vitro. While transfer of spleen cells from TI-Mice resulted in the suppression of IFN production in normal mice (N-Mice) stimulated with IFN-gamma inducers, the transfer of spleen cells derived from TGe-Mice did not induce suppression of IFN production in N-Mice. Mononuclear cells (MNC) prepared from N-Mice produced IFN following concanavalin A (Con A) stimulation when they were co-cultured with macrophage-enriched populations (PAC) obtained from the spleens of TGe-Mice. In contrast, MNC stimulated with Con A did not produce IFN activity when they were co-cultured with PAC of TI-Mice. These results suggest that the generation of suppressor macrophages in TI-Mice may be altered by the administration of Ge-132.