BACKGROUND: T lymphocytes play a crucial role in the pathogenesis of inflammatory bowel disease. Achieving stable T-cell lines, rather than continuous bleeding of patients, is desirable in order to dissect their implication in the disease. METHODS: Long-lasting T-cell lines from patients with Crohn disease and ulcerative colitis and from healthy volunteers have been obtained by transformation of T lymphocytes using the lymphotropic Herpesvirus saimiri. Lines were subjected to phenotypic and functional analyses, and the results compared with freshly isolated peripheral blood mononuclear cells. RESULTS: Fresh cells revealed only minor differences between patients and controls, with regard to phenotype and proliferative capacity. In contrast, the use of T-cell lines showed that cells from Crohn disease patients, but not ulcerative colitis patients, over-responded to several membrane or cytoplasmic stimuli when compared to control T-cell lines. Thus, higher responses were found when stimulated with alphaCD3 and IL2, alphaCD3 and alphaCD28, IL2 alone, phorbol esters (PMA) and alphaCD3 and, finally, PMA and alphaCD2 (P < 0.05 in all instances). Further, lines from patients with Crohn disease responded more vigorously to alphaCD3 and alphaCD28 or alphaCD3 and PMA when compared to ulcerative colitis (P < 0.05 in both instances). CONCLUSIONS: The data obtained with these lines suggest that T cells from patients with Crohn disease differ in vivo in their proliferative capacity, as compared with those from ulcerative colitis patients, a finding that may reflect the clear Th-1 phenotype found in the former and absent in the latter.