INTRODUCTION: T-cell KV1.3 and KCa3.1 channels have been proposed to be important effector proteins during T-cell activation and also in autoimmune disease by controlling T-cell motility, cytokine production, and proliferation. The role of KV1.3 channels in ulcerative colitis (UC) has not been defined yet. In the present study we hypothesized that T-cell KV1.3 and KCa3.1 expression may serve as novel molecular marker for T-cell infiltration, inflammatory activity, and possibly disease progression. AIMS & METHODS: Biopsies were obtained from the rectal mucosa in seven UC patients with clinical and endoscopic active disease and seven non-UC patients. Active inflammation in the rectal mucosa in patients with UC was verified histologically. Expression of KV1.3 and KCa3.1 genes and of INFγ as a classical marker of inflammation was investigated in mRNA-extracts from biopsies by quantitative RT-PCR (qPCR). RESULTS: Expression of KV1.3 was significantly ~7-foldly increased in UC patients compared to the very low background expression in controls (P<0.05). KCa3.1 gene expression tended also to be 2-foldly increased in UC patients compared to the basal physiological expression in intestinal epithelium of controls (P=0.1). Expression of INFγ as classical marker of inflammation was also ~10-fold increased in UC patients compared to the very low background expression levels found in non-UC controls (P<0.05). CONCLUSION: Expression of KV1.3 and, possibly, KCa3.1 channels are increased in a disease related fashion in UC patients and may point to an increased infiltration and activity of effector T-cells and effector memory T-cells in UC. These markers could be predictive of progression and for adjusting individual immune suppressive treatments.