The current studies were carried out to determine the expression of Fas ligand and Bax in kidneys from lupus nephritis as possible indicators of apoptosis. Twenty-four kidney biopsies from patients with lupus nephritis and 30 normal controls were studied for FasL and Bax gene expression by fluorescent in situ hybridization. Seventy percent of the lupus biopsies displayed FasL or Bax mRNAs. These genes were mainly expressed in biopsies with higher activity indices. In contrast, neither of these mediators was detected in normal glomeruli. These data suggest that FasL and Bax are up-regulated in lupus nephritis and may play a pathogenic role through apoptotic cascades.