There is evidence that the production of primary saliva by acinar cells is a consequence of Na+−Cl− co-transport but more recently it has been proposed that in fact Na+−K+−2 Cl− co-transport is responsible. The latter would be energetically more efficient and the present experiments were designed to measure the stoichiometry of acinar secretion in order to distinguish between these two mechanisms. Submandibular salivary glands from anaesthetised rabbits were isolated vascularly and oxygen consumption measured from the oxygen content of arterial inflow and venous effluent blood and the total flow through the gland. Measurements were made in the steady-state at rest and during different secretion rates induced by parasympathetic nerve stimulation. The rate of sodium transport across the acinar and ductal epithelium was determined from plasma and salivary sodium concentration and salivary flow rate. Multiple regression analysis of this data showed that 22.1 mol Na+ was secreted per mol O2 consumed while 11.9 mol Na+ was reabsorbed per mol O2 consumed. Since acinar secretion is energetically about twice as efficient as ductal absorption, a mechanism for Na+ transport other than that for tight epithelia must be involved. Na+K+−2 Cl− co-transport is thus more likely than Na+−Cl− and it is suggested that Na+−K+−2 Cl− co-transport is the main mechanism involved in salivary acinar secretion.