Thiazide diuretics are among the first-line alternatives in the treatment of primary hypertension. The effects of thiazide treatment on salivary production are, however, little studied and the results so far available are not decisive. The aim of the present study was to evaluate and compare salivary flow rate and composition during treatment with the thiazide diuretic bendroflumethiazide in a low dose (2.5 mg o.d.) and placebo. The study was performed with a randomized, double-blind, cross-over design (2 x 2 wk) in 34 healthy volunteers. The treatment periods were separated by a wash-out period of 2 wk. Resting and stimulated whole saliva was sampled three times daily on scheduled days during the treatment periods. Flow rate was assessed for resting saliva, whereas flow rate, pH, buffer capacity, amount of total proteins and concentrations of sodium, potassium, calcium, phosphate and magnesium were measured for stimulated whole saliva. No effect of bendroflumethiazide on the resting salivary flow rate could be detected, while the stimulated flow rate was significantly reduced by about 10% during the thiazide treatment. The total sodium output was significantly decreased by approximately 30%, without any detectable change in total potassium output. All other variables of stimulated whole saliva studied were not different from placebo. It is concluded that treatment with bendroflumethiazide in a low dose significantly reduces the stimulated whole salivary flow rate and total sodium output in healthy volunteers.