The human colonic epithelial cell line Cl.16E grows in culture as a polarized monolayer which differentiates at confluency into typical goblet cells secreting their mucin content into the culture medium. Polyclonal antibodies raised against these mucins were used in an ELISA to measure the amount of mucins secreted by the Cl.16E cells. Carbachol caused a transient and significant increase in mucus secretion with a maximal stimulation occurring at 30 min. A dose-dependent effect was found with a maximal stimulation with 10-3M carbachol. This effect was inhibited by atropine. These results indicate that the effects of carbachol are mediated by muscarinic receptors present on mucus-secreting epithelial cells.