Cell swelling-induced exocytosis of material stored in intracellular vesicles is a broad phenomenon affecting many hormones and enzymes after exposure of the cells to relative hyposmosis or permeant treatment. This study was undertaken to investigate the effect of hypotonicity and permeants in isosmotic medium on insulin release from rat insulinoma cell line INS-1E. By means of confocal microscopy, the increase of volume of cells exposed to hypotonic medium was demonstrated. Perifusion of cells revealed stimulation of insulin release by glucose but not by hypotonic medium. In static incubations both hypotonic medium and urea inhibited insulin secretion. Unexpectedly, another permeant, ethanol, stimulated insulin release. Taken together, INS-1E cell line does not release insulin in response to swelling induced by hypotonicity. Different effect of urea and ethanol on insulin secretion suggests involvement of different mechanisms. Acknowledgements: We thank Dr. Claes B. Wolheim, University Medical Center, Geneva for providing us with INS-1E cell line. Supported by 23191/23 of the Grant Agency VEGA, APVT-51016002 and SP 51/0280800/0280802.