SummaryA double-blind trial of reserpine and propranolol as adjuncts in the treatment of hyperthyroidism is described. Eighteen previously untreated hyperthyroid patients took part in the trial on an out-patient basis. Reserpine was given on an oral dosage of 0.25 mg. 4-times daily while propranolol was given on an oral dosage of 40 mg. 4-times daily; each drug was given for a period of 2 weeks. There was no significant difference in the effect of reserpine and propranolol on the symptoms, signs and certain investigations of hyperthyroidism. Two patients on reserpine complained of diarrhoea while 3 patients on propranolol had insomnia. It is concluded that the choice between reserpine and propranolol as an adjunct in the treatment of hyperthyroidism is dependent on their side-effects; bronchial asthma is the major contra-indication to propranolol while mental depression is the major contra-indication to reserpine.