Concentrations of interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-alpha (TNF-alpha) were determined by solid-phase ELISA in tissue homogenates of mucosal biopsy specimens obtained from pelvic ileal pouches in 13 patients with pouchitis (reservoir ileitis) and 17 with pouches without pouchitis. Normal ileal mucosa was used as a control. IL-1 beta was detected in all tissue homogenates from patients with pouchitis compared with only 29% from pouches without pouchitis and none from controls. IL-6 and IL-8 were present in all pouchitis specimens, in 70% of the specimens from nonpouchitis and only 30% of specimens from controls. TNF-alpha was undetectable in all specimens examined. The concentrations of IL-1 beta, IL-6, and IL-8 were significantly greater (P < 0.001) in biopsy specimens from pouchitis compared to those from pouches without pouchitis or normal ileal mucosa and in patients with pouchitis tissue levels of IL-1 beta significantly correlated with IL-6 (P < 0.05) and IL-8 (P < 0.01). Furthermore IL-1 and IL-8 levels were significantly higher in tissue specimens from nonpouchitis pouches than in those from normal ileal mucosa (P < 0.02). These results suggest that an enhanced cellular immunity operates in vivo at the mucosal level in pouchitis as in the case of ulcerative colitis.