Monocytes have been demonstrated to play an important role in acute serum sickness (AcSS) nephritis. Because accumulation of monocytes within the glomeruli could be the result of local lymphokine production, we studied migration inhibition factor (MIF) activity in supernatants from glomerular cultures, analyzed its temporal relationship with monocyte and lymphocyte accumulation, and tested the effect of anti-T lymphocyte monoclonal antibody on local MIF production. AcSS was induced in 12 rabbits, and one additional rabbit had antigen elimination without proteinuria. Single nephrectomy was performed at the time of antigen elimination in all animals; the remaining kidney was removed four days (4 rabbits) or 14 days afterwards (5 rabbits). In glomerular cross sections (gcs), lymphocytes were identified using monoclonal antibody M108, and monocytes by nonspecific esterase stain (ES). MIF activity was determined in supernatants of cultures of isolated glomeruli by the agarose microdroplet method. Peak of MIF activity (84.3 ± 2.6%, SEM) was observed the first day of proteinuria in association with peak of lymphocyte infiltration (1.15 ± 0.1 lytnphocytes/gcs) and monocyte infiltration (2.4 ± 0.3 mean ES score/gcs). MIF activity diminished by day 4 (66.0 ± 6.3%) and reached control levels by day 14 (12.8 ± 3.2%). There was a significant correlation between lymphocyte infiltration and MIF activity (r = 0.776, P < 0.0001) as well as between MIF activity and monocyte accumulation (r = 0.858, P < 0.0001). In five additional rabbits with AcSS, glomeruli were isolated, treated successively with M108 and normal rabbit serum, and supernatants harvested from 24-hour cultures were tested for MIF activity. Negative controls were supernatants treated with T1-lytic monoclonal antibody, as well as untreated glomerular cultures. MIF activity from untreated and T1-lytic treated glomerular cultures was similar. Addition of M108 monoclonal antibody to glomerular cultures produced 70 ± 12.9% inhibition of MIF activity. Our data suggest that lymphocytes infiltrating the glomeruli in AcSS produce lymphokines (MIF) which are related to the monocyte accumulation.