Both 86Rb and 42K appeared to serve as useful markers for potassium movements in rat parotid gland slices. Carbachol and phenylephrine elicited a biphasic increase in potassium release (86Rb release) that was dose related and could be blocked by atropin and phentolamine, respectively. The early transient phase of 86Rb release lasted from 3 to 6 minutes and was not blocked by removal of external Ca. These observations suggested that the transient phase corresponded to the transient hyperpolarization seen by others in response to alpha adrenergic or cholinergic agents. The latter sustained phase of 86Rb release was qualitatively blocked by chelation of external Ca ions or by 1 mM LaCl3. Thus, the sustained phase of release appeared to relate to the loss of total potassium seen by others with this tissue and to the mechanisms responsible for transporting water from blood to saliva.