Nuclear autoantigens from apoptotic cells are believed to drive the immunological response in systemic lupus erythematosus (SLE). Conflicting data exist as to the possible renal origin of apoptotic cells in SLE patients with nephritis. We assessed the level of renal cell apoptosis in kidney biopsies from 35 patients with lupus nephritis by means of terminal deoxynucleotidyl-transferase (TdT)-mediated deoxyuridine triphosphate (dUTP)-digoxigenin nick end labeling (TUNEL). Five samples of normal kidney tissue served as control specimens. We did not observe apoptotic glomerular cells in any of the control or nephritis biopsies. Scarce apoptotic tubular cells were seen in 13 of 35 (37%) of the nephritis specimens and in two of five (40%) of the control sections. Within the SLE cohort, patients with TUNEL-positive tubular cells in their renal biopsies had significantly higher activity index scores for tubulointerstitial mononuclear cell infiltration than patients without apoptotic tubular cells in their biopsies (P = 0.01). Furthermore, the level of tubular cell apoptosis displayed a statistically significant, positive correlation with the activity index score for mononuclear cell infiltration (r(s) = 0.472, P = 0.004) but not with scores for other activity or chronicity index components. These observations indicate that the degree of tubular cell apoptosis correlates with the severity of tubulointerstitial inflammation in SLE-associated nephritis. However, our findings do not suggest that apoptotic renal cells constitute a quantitatively important source of auto-antibody-inducing nuclear auto-antigens in human lupus nephritis.