The effect of 1600 mg/day ibuprofen in two groups of patients with hypertension controlled by either propranolol or bendrofluazide was studied in a double-blind, double-placebo, randomized crossover trial. No significant difference in blood pressure was found at the end of the crossover period in either group, suggesting that the routine co-administration of ibuprofen does not attenuate the anti-hypertensive effect of thiazide diuretics or propranolol. Significant weight gain, attributable to fluid retention, had occurred in the bendrofluazide-treatment group by the end of the drug-free washout period. No significant change in mean weight occurred in the crossover stages in either group, although substantial weight gain was noted during ibuprofen treatment in two patients given bendrofluazide and one given propranolol. Biochemical variables were unaffected by ibuprofen throughout the crossover period. This study suggests that ibuprofen may be administered routinely to patients receiving thiazides or propranolol without loss of control of the anti-hypertensive action of these drugs but it is recommended that individuals are monitored for possible weight gain or an increase in diastolic blood pressure.