The purpose of this study was to investigate the effects of caloric vestibular stimulation on the postural sway characteristics of hemiparetic patients. Two groups of 15 hemiparetic patients each (right and left) were compared to a group of 15 control subjects. Hemiplegic patients were selected for the study if they showed ability to stand without external support for at least 30 seconds. Posturographic evaluation was performed on a statokinesimetric platform just before and after a cold contralesional ear irrigation (20 degrees C) during 60 seconds. Two quantitative parameters were analysed: the antero-posterior difference and the lateral difference, reflecting the asymmetry of standing in the antero-posterior and frontal planes, respectively. The results of the 3 groups studied were compared with a Student's t-test. Before stimulation, as previously reported, left hemiparetic patients showed a predominant lateral displacement of the centre of pressure toward the side of the lesion, as compared to right hemiparetic patients. After vestibular stimulation, the lateral displacement was reduced in both patient groups, predominantly in the left hemiparetic group. After vestibular stimulation, the lateral displacement thus was not different in both patient groups and in the control group. Antero-posterior differences were not significantly different in the patient groups and in the control group before stimulation and were not affected by vestibular stimulation. The suggestion is made that greatest postural imbalance produced by right brain damage could reflect a persistent distorsion of a "spatial postural representation". Vestibular stimulation may restore symmetrical activity in the cerebral structures involved in the generation of this "spatial postural representation".