20 normal healthy subjects in a double-blind crossover experiment were given a tablet of either 40 mg propranolol or placebo half an hour before the beginning of the experiment. At rest and during the performance of a task, heart rate, Achilles tendon (T) and Hoffmann (H) reflexes were recorded. No increase in heart rate occurred during the task in the propranolol session. The increase of T-reflex amplitude, a common finding during the task under consideration, was larger in the propranolol session. No difference with H reflexes was found. It is concluded that the increase of T-reflex amplitudes during the task is caused only by fusimotor and not by sympathetic activity. It is speculated that if the sympathetic system plays a role at all, the effect on the T reflex is depressive rather than facilitating.