The aim of the present study was to investigate whether the IL-1 family cytokines, in addition to IL-6 and IL-8, could be induced in normal human cortical epithelial cells in response to bacterial stimuli. Human renal tissue was obtained from 9 patients undergoing elective tumour nephrectomy. Renal cortical epithelial cells of tubular origin were prepared from the unaffected tissue. The proximal tubular cells were stimulated for 2, 6 and 24 h with a heat-inactivated pyelonephritogenic Escherichia coli strain DS-17. Cultured unstimulated tubular cells served as controls. IL-1α, IL-1β, IL-1 receptor antagonist, IL-6, IL-8, IL-10, TNF-α, G-CSF and GM-CSF were analysed using immunohistochemistry at the single cell level. The nonstimulated cells were found to express low levels of IL-6 and IL-8 (mean value < 3% of total cells). In contrast, E. coli exposure resulted in significantly increased incidences of IL-6 and IL-8 expressing cells (mean values ≈18% of total cells) peaking within two hours of stimulation (P < 0·008 and P < 0·02 versus non-stimulated cells, respectively). A gradual decrease was thereafter observed at 6 and 24 h, respectively, although persistently higher compared to controls. A different kinetic response was found for IL-1α, IL-1β and IL-1 receptor antagonist-expressing cells, which peaked 24 h after E. coli stimulation (mean values 3–10%) (P < 0·008, P < 0·02, P < 0·02 versus non-stimulated cells, respectively). Low levels of TNF-α and GM-CSF were found in 3 of the 9 donated epithelial cells, peaking at 2 h, and IL-10 and G-CSF producing cells in 1 patient each. In conclusion we found that heat-inactivated pyelonephritic E. coli induced a proinflammatory cytokine response in the normal human proximal tubular cells including the IL-1 family, IL-6 and IL-8.