A systematic clinical study of certain defined types of `extra-pyramidal' motor phenomena was carried out in a population of 63 chronic hospitalized schizophrenics who had been treated with trifluoperazine for periods ranging from 3 to 13 years. Tremor was found in 88 per cent, muscular rigidity in 68 per cent, choreiform dyskinesia in 56 per cent, and motor restlessness in 38 per cent. The clinical data were submitted to factor analysis in order to identify the principal patterns of motor disorder affecting these patients. Sex, age, state of dentition, as well as phenothiazine and anti-parkinsonism drug treatment variables were then studied in relation to the distributions of the motor disorders suggested by factor analysis.

Factor 1, which accounted for 32.5 per cent of the variance, represented restlessness of the trunk and limbs. The distribution of this disorder in the population was not affected by any of the personal and treatment variables studied.

Factor 2 accounted for 19.1 per cent of the variance and represented tremor and rigidity of the upper limbs and facial musculature. This disorder was significantly more common in older patients.

Factor 3 was bipolar and contributed 13.0 per cent to the variance. It suggested a disorder of the tongue, lips and jaw characterized by choreiform movements at one pole negatively correlated with tremor at the other pole. Chorea was more common and tremor less common in women than in men. For men, though not women, chorea was associated with a low total dose of phenothiazine and tremor with a high total dose.

The usefulness of this method and the implications of our results are discussed, particularly with respect to choreiform disorders which may be irreversible.