Objective: Epithelia separate different fluid compartments and determine the respective salt composition. In addition they take part in the innate immune system being a physical barrier and secreting substances with antimicrobial activity. Human b-defensin 2 (hBD-2) is an inducible peptide of epithelia with a broad antimicrobial spectrum. We hypothesize that hBD-2 itself modulates the ion transport properties of colon epithelial cells in a feedback mechanism, thereby integrating epithelial cell function into the immune response. Methods: We tested the effect of hBD-2 in Ussing chamber experiments (luminal application) on native rat distal colon and by fura-2 measurements in the colon carcinoma cell line HT29. 20min after peptide application a cholinergic response was induced by 100mmol/l carbachol (CCh). In HT29 cells we investigated the concentration response and the dependence on extracellular Ca²⁺ (10^-7mol/l), thapsigargin (1mmol/l) and ionomycin (2mmol/l). Results: 10mg/ml hBD-2 showed no acute effect in both tissues. After preincubation, hBD-2 enhanced the CCh induced increase in equivalent short-circuit current in distal colon by 50%. In HT29 cells, the effect of hBD-2 on CCh induced Ca²⁺ increase was concentration dependent. EC50 was 0.043mg/ml and the maximal increase of 20-30% occurred at a concentration of 1mg/ml. This effect was reproducible in the absence of extracellular calcium. hBD-2 preincubation did not alter the effect of thapsigargin whereas the ionomycin induced Ca²⁺ transient was equally enhanced. Conclusion: hBD-2 modulates the cholinergic response in epithelial cells via interference with intracellular Ca²⁺ signaling. This suggests that hBD-2 can act as a paracrine hormone-like messenger substance, in addition to its immunological properties.