Serum thyroid hormone concentrations were measured before and during 6 months 
treatment with propranolol (160 mg/day) in eight patients with T3 
(triiodothyronine) toxicosis. Serum total T3 concentrations showed a significant 
(p less than 0.01) and sustained fall to approximately 80% of pre-treatment 
values. Six of the patients, however, remained clinically and biochemically 
hyperthyroid and our data do not support the use of propranolol as sole therapy 
in T3 toxicosis.