Concentrations of interleukin-1 beta (IL-1 beta), interleukin-2 (IL-2), and soluble IL-2 receptors (sIL-2R) were determined by enzyme linked immunosorbent assays (ELISA) in supernatants of sonicated endoscopical mucosal biopsy specimens from 31 patients with inflammatory bowel disease and 19 controls. IL-1 beta was detected in 53% of the patient supernatants (p = 0.0001), IL-2 in 35% (p = 0.0031), compared with none of the controls. Soluble IL-2R was present in 55% and 26% of the specimens, respectively (p = 0.07). The concentrations of IL-1 beta (p = 0.00015), IL-2 (p = 0.0019), and sIL-2R (p = 0.0073) were highest in the most inflamed biopsy specimens, compared with less inflamed specimens and controls. There were no significant differences in IL-1 beta, IL-2, and sIL-2R concentrations between ulcerative colitis (16) and Crohn's disease patients (15). The results suggest that enhanced cellular immunity operates in vivo at the mucosal level in active inflammatory bowel disease.