Isolated salivary glands of Periplaneta americana were used to measure secretion rates and, by quantitative capillary electrophoresis, Na + , K + , and Cl - concentrations in saliva collected during dopamine (1 μM) and serotonin (1 μM) stimulation in the absence and presence of ouabain (100 μM) or bumetanide (10 μM). Dopamine stimulated secretion of a NaCl-rich hyposmotic saliva containing (mM): Na + 95 +/- 2; K + 38 +/- 1; Cl - 145 +/- 3. Saliva collected during serotonin stimulation had a similar composition. Bumetanide decreased secretion rates induced by dopamine and serotonin; secreted saliva had lower Na + , K + and Cl - concentrations and osmolarity. Ouabain caused increased secretion rates on a serotonin background. Saliva secreted during dopamine but not serotonin stimulation in the presence of ouabain had lower K + and higher Na + and Cl - concentrations, and was isosmotic. We concluded: The Na + -K + -2Cl - cotransporter is of cardinal importance for electrolyte and fluid secretion. The Na + /K + -ATPase contributes to apical Na + outward transport and Na + and K + cycling across the basolateral membrane in acinar P-cells. The salivary ducts modify the primary saliva by Na + reabsorption and K + secretion, whereby Na + reabsorption is energized by the basolateral Na + /K + -ATPase which imports also some of the K + needed for apical K + extrusion.