The effects of piperidine HCl (PHCl) on locomotor activity, flexor reflex activity and monoamine levels, turnover, and synthesis were studied. Results indicate a sedative action and an increased turnover of noradrenaline (NA), but no effects on 5-hydroxytryptamine (5-HT) or dopamine (DA). Data obtained from flexor reflex experiments suggest that this is not secondary to alpha-adrenergic receptor blockade. One explanation might be an increased impulse activity of NA neurons, but the exact mechanism remains to be elucidated.