1. Beta-adrenoceptor blockade with propranolol (40 mg, 6 hourly) did not significantly decrease thermal or mental sweating in a group of eight thyrotoxic patients.
2. The patients did not appear to sweat excessively either when at rest in an environmental temperature of 29°C or in response to mental arithmetic when compared with a group of young healthy medical students.
3. A state resembling thyrotoxicosis was induced in two healthy subjects by the oral administration of tri-iodothyronine (T3) over a period of days.
4. This increased the sweat response to thermal stress but did not precipitate active sweating in an environmental temperature of 29°C.
5. Neither oral propranolol therapy during T3 administration nor intravenous injection of propranolol significantly decreased the induced sweat response to thermal stress.