Trihexyphenidyl, a synthetic anticholinergic, used to control extrapyramidal symptoms arising from neuroleptic drug therapy has been a subject of controversy regarding the need for continuous antiparkinsonian therapy. In a group of 22 psychiatric patients receiving long-term antipsychotic medication concurrently with trihexyphenidyl the effects of trihexyphenidyl withdrawal were studied double-blind and placebo controlled. Anxiety, psychotic symptoms, extrapyramidal symptoms and salivary flow were monitored. Blood pressure, pulse, sleep duration, weight and body temperature were recorded daily. The result was a recognizable withdrawal syndrome indicated by an increase in anxiety with various physical complaints, as well as evidence of orthostatic hypotension and tachycardia. A temporary deterioration was noted in psychotic symptomatology and extrapyramidal symptoms. The majority of the parameters regained baseline values, indicating the symptoms were related to the discontinuation of trihexyphenidyl and supporting the existence of a withdrawal syndrome.