Besides their role in ion transport and homeostasis epithelia provide a first defense barrier. In addition to their physical properties epithelia secrete antimicrobial peptides (AMPs) as part of the innate immune response. Some AMPs are constitutively expressed, others induced by pro-inflammatory cytokines or bacterial products. We hypothesize that AMPs influence epithelial function to provide a feedback signal modifying luminal fluid composition. We tested the luminal effects of human b- defensin-2 (hBD-2) on native, freshly isolated rodent tissues in Ussing chamber experiments as well as on the human colonic carcinoma cell-line HT-29, using the patch clamp technique and fura-2 Ca2+ measurements. Acute administration of hBD-2 did not alter colonic cAMP-stimulated chloride secretion, electrophysiological cell properties or intracellular Ca2+ activity. Only a slight and transient increase in tracheal short-circuit current (I´sc ) was observed. After a 20min pre-incubation period hBD-2 led to an increased cholinergic response in the presence of cAMP stimulation in rat distal colon (vehicle: 189 ± 22 vs. hBD-2: 261 ± 21 % change in I´sc ). In corresponding Ca2+ measurements in HT-29 cells hBD-2 resulted in an increase of the CCH induced Ca2+ transient (peak-ratio vehicle: 1,73 ± 0,05 vs. hBD-2: 1,98 ± 0,06). Taken together our data suggest the presence of a feedback signal of AMPs on epithelial function, which seems to be beyond the acute pore-forming properties of hBD-2.