A study was carried out to determine whether beta-adrenergic hypersensitivity occurs in normal subjects following the abrupt withdrawal of the beta-adrenoceptor antagonist propranolol. Sixteen normal subjects took propranolol, orally, 120 mg twice daily for one week. Heart rate and blood pressure were measured supine and standing as well as during exercise. Heart rate was measured during and following the Valsalva manoeuvre. Measurements were made on the last day of the treatment period and on two occasions during the six days following withdrawal. Three subjects were removed from the analysis because of failure to take medication and one more was excluded because of protocol variation. In the remaining twelve, propranolol treatment reduced all parameters measured. Following abrupt withdrawal of the drug, there was no measurable increase in any of the parameters above baseline or placebo values within six days of the withdrawal. These findings, from normal subjects, do not support the phenomenon of beta-adrenergic hypersensitivity following propranolol withdrawal.