The cell-attached and excised patch configurations of the patch clamp technique were used to study stretch-activated ion channels in Muller glial cells that were obtained from postmortem adult human retinas and were maintained in culture. A stretch-activated channel permeable to monovalent and divalent cations was found. Ion channels of this type have not been demonstrated previously in glial cells, though indirect evidence has suggested that such stretch-activated channels may help mediate a compensatory response of glia to swelling. Consistent with a possible role for volume regulation is the finding that the activation of calcium-permeable stretch-sensitive channels is associated with an increase in the activity of calcium-activated potassium channels. Activation of potassium channels to produce an efflux of potassium with a subsequent loss of anions and cell water could be an effective mechanism to decrease glial cell volume.