The roles of potassium and chloride ions in cAMP-mediated amylase exocytosis were studied using intact and saponin-permeabilized parotid acini. Cyclic AMP-evoked amylase release from saponin-permeabilized parotid acini decreased markedly when KCl in the incubation medium was isoosmotically replaced by K-glutamate, NaCl, Na-isothionate, or mannitol. Quinidine and barium, K+ channel blockers, clearly inhibited amylase release from the permeabilized acini, but not from intact ones. The chloride channel blocker DPC (diphenylamine-2-carboxylate) also inhibited amylase release, while DIDS (4,4'-diisothiocyanostilben-2,2'-disulfonate) or bumetanide had little effect, if any, on the exocytosis. Hyperosmolarity with mannitol markedly reduced amylase release from permeabilized acini. These results suggest that potassium and chloride ions play important roles in cAMP-mediated amylase exocytosis, and that these ions act on secretory granules inside the acinar cells.