20 microgram TRH injected bilaterally into the caudate-putamen, tuberculum olfactorium, nucleus accumbens, amygdala, lateral ventricles, midbrain or cerebral cortex failed to induce any increase in locomotor activity (measured using photocells), although other behavioural changes were observed after each injection, and included body shakes, limb tremor, repetitive head and limb movements, biting, scratching and an alert appearance. These behavioural changes could result in positive readings from equipment used to measure locomotor activity, but careful investigations focussing on the nucleus accumbens used photocell boxes, activity wheels and Animex recorders to emphasise the inability of intracerebral TRH (10--40 microgram) to enhance locomotor activity. Intraaccumbens TRH also failed to enhance amphetamine hyperactivity or reduce the motor depression caused by haloperidol and analeptic drugs. The data do not support a central locomotor stimulant action of TRH.