The possibility that intranasally administered phenylephrine might cause systemic vasoconstriction and an important increase in blood pressure if administered to susceptible individuals in higher doses was investigated in two groups potentially at high risk: 12 patients with chronic nasal congestion whose blood pressure was normal and 14 patients with hypertension receiving the beta-blocker metoprolol. On two separate days increasing doses (0.5 to 4 mg) of phenylephrine or a placebo of identical appearance were instilled into the nostrils at hourly intervals. The blood pressure and the heart rate were recorded every 10 minutes. The total amount of phenylephrine administered (7.5 to 15 mg) was 4 to 30 times the manufacturer's recommended dose. No significant changes in blood pressure or heart rate occurred in either group after the instillation of phenylephrine.