Although the main function of the colon is salt and water absorption, it has the capacity to secrete substantial amounts of K⁺ and Cl in infective and neurohumoral diarrhoeal diseases. Secretion involves movement of ions across the luminal (apical) membrane of colonic crypt cells, K⁺ exiting via large conductance K⁺ (BK) channels and Cl^– through CFTR. Colonocytes and goblet cells constitute most of the crypt cell mass. It is generally assumed that both K⁺ secretion and Cl^– secretion arise from colonocytes in response to the activation of different second messenger cascades, but the relative magnitudes and spatial arrangement of the apical K⁺ and Cl^– conductances are unclear. Intact crypts were isolated from distal colonic biopsies obtained with consent from patients undergoing routine colonoscopy for altered bowel habit, in whom the mucosa was macroscopically and histologically normal. Whole-cell K⁺ and Cl^– currents and conductances were measured from the mid-third of colonic crypts using the perforated patch technique (addition of amphotericin B to the pipette). Comparisons were made using Student’s t-test. Two distinct cell populations were identified based on the biophysical characteristics, pharmacology and agonist responses of the whole-cell currents. 73% of cells (58/79) had basal inwardly rectifying K⁺ conductances (IR), which were 68 ± 14% (P<0.05, n = 4) inhibited by clotrimazole (10μM), a blocker of intermediate conductance IK channels, but not by penitrem A (100nM), a blocker of BK channels. In contrast, 27% (21/79) of cells had a basal outwardly rectifying K⁺ conductance (OR) which was 68 ± 6% (P<0.005, n = 8) inhibited by penitrem A. Stimulating intracellular cAMP activated CFTR in IR cells (whole-cell conductance increasing from 0.97 ± 0.1nS to 3.5 ± 0.5nS, P<0.0005, n = 11), but had no effect in OR cells (6.6 ± 1.0nS to 7.3 ± 1.0nS, n = 7). We conclude that K⁺ and Cl^– secretion occur in different cell types within colonic crypts. Given the relative proportions of colonocytes and goblet cells within the human colon, our data suggest that goblet cells are the main site of K⁺ secretion, whereas colonocytes are the main site of Cl^– secretion.