Skin reactivity to dinitrochlorobenzene (DNCB) and levels of circulating T-lymphocytes were measured in 15 patients with ulcerative colitis, 15 patients with Crohn's disease, and 12 normal control subjects. Diminished reactivity to DNCB was demonstrated in 87% of patients with Crohn's disease (p < 0.001) and in 53% with ulcerative colitis (p < 0.02), as compared with only 8.5% of controls; anergy was more frequent in Crohn's disease than in ulcerative colitis (p < 0.05). Levels of circulating T-lymphocytes were also depressed in both Crohn's disease and ulcerative colitis (P < 0.001) as compared with controls, with the values lower in Crohn's disease than in ulcerative colitis (P < 0.02). There were no correlations of DNCB response with extent, duration, or severity of disease nor with T-cell levels within any patient group. These data provide further support for the concept that there is impairment of cell-mediated immunity among many patients with chronic inflammatory bowel disease, including both Crohn's disease and ulcerative colitis.