Mice deficient in both interleukin-2 and beta 2-microglobulin expression (Beta 2mullnull x IL-2null mice) develop an inflammatory disease of the colon resembling ulcerative colitis. To examine long-term complications of disease in these mice, a group of 34 Beta 2mnull x IL-2null mice was monitored for 6-12 months. Development of clinical disease was assessed by wasting, general appearance, and diarrhea. Further analysis included histologic examination of the distal colon for colitis, staining of CD4+ T cells for surface activation markers, and cytoplasmic staining of CD4+ T cells for IFN-gamma and TNF-alpha. These older Beta 2mnull x IL-2null mice had activated CD4+ T cells as assessed by surface markers on flow cytometry. Cytoplasmic staining revealed IFN-gamma production, but not TNF-alpha production by CD4+ T cells. The majority of these older Beta 2mnull x IL-2null mice continued to have colitis on histology. However, they lived much longer and had less wasting in comparison to IL-2null mice. At necropsy, 11 (32%) of 34 of the Beta 2mnull x IL-2null mice had tumors in the proximal half of the colon. Histologic examination confirmed these tumors to be adenocarcinomas. These mice may be useful as a model for studying carcinogenesis in chronic colitis.