The production of cytokines in peripheral blood mononuclear leukocytes of patients with inflammatory bowel disease was investigated. T cell subset analysis and differential white blood cell counts were also performed. Thirty five patients with ulcerative colitis, 14 with Crohn's disease, and 15 age matched healthy volunteers were studied. No differences were observed in T cell subsets and OKT4/OKT8 ratios in patients with ulcerative colitis or Crohn's disease compared with controls. Interleukin 1 beta production was significantly increased in active ulcerative colitis and Crohn's disease, compared with values in controls, but returned to control levels in the inactive stages. In addition, in active ulcerative colitis and Crohn's disease, there were significant correlations between the interleukin 1 beta production and the ulcerative colitis activity index or Crohn's disease activity index. Interleukin 2 production was also significantly increased in the active ulcerative colitis and significantly correlated to the activity index, but there was no change in Crohn's disease patients compared with controls. Gamma interferon production in patients was the same as that in controls. This study suggests that the interleukin 1 beta and 2 values in peripheral mononuclear leukocytes of active untreated inflammatory bowel disease are indicators of the disease states of ulcerative colitis or Crohn's disease, or both.