Delivery of modified Krebs-Henseleit solution (MKHS) of raised osmolarity (added NaCl or KCl) to the lumen of methacholine (MCh)-contracted IPT results in a relaxation response of the airway smooth muscle that is mediated by epithelium-derived relaxing factor (EpDRF). We compared the effects of luminally-applied solutions containing organic osmolytes added to MKHS to raise osmolarity (hypertonic solutions) or isotonic solutions to the osmolytes. As has been observed previously with NaCl and KCl, solutions made hypertonic with urea, mannitol, N-methyl-D-glucamine-Cl (NMDG) and Na-gluconate (Glu) elicited osmolar concentration - dependent relaxations of MCh (3 x 10^-7 M) - contracted IPT when applied to the mucosal surface. To determine if relaxation responses caused by hypertonic solutions involved airway epithelial cell shrinkage, IPT were challenged intraluminally with isotonic mannitol, urea, NMDG, Glu or NaCl. Generally, mannitol, NMDG, and Glu evoked complex responses containing contraction and relaxation. Urea caused contraction or relaxation in different tracheas. NaCl was primarily relaxant. These findings suggest that EpDRF release in response to hypertonicity does not result from cell shrinkage per se, but may be due to altered ion fluxes.