Calcium-activated potassium currents of intermediate conductance (IK1) have been described in the rodent enteric nervous system, where they may regulate afterhyperpolarisation of intrinsic primary afferent neurons. Using specific antibodies for immuno-cytochemistry, we now report IK1-like immunoreactivity for the first time in enteric neurons of human colon, and a significant decrease of IK1-positive cells in myenteric plexus in inflamed colon from patients with Crohn's disease and ulcerative colitis (p = 0.031). Neurotrophin-3 (NT-3), which regulates IK1 expression, was also observed in fewer neurons of the myenteric ganglia in Crohn's bowel (p = 0.048), and in inflamed colonic extracts by Western blotting (p = 0.004); the numbers of neurons expressing the NT-3 high affinity receptor trk C were unchanged. Our findings may explain the diarrhoea and colicky abdominal pain produced by inflammatory bowel disease, and by IK1-blocking pyridine drugs prescribed for neuromuscular disorders.