The authors report three patients suffering since infancy from transient attacks of paresis. The flaccid pareses most frequently affect the extremities in a hemiplegic fashion, but occasionally there is monoparesis or quadriparesis. The laterality and degree of the paresis are variable. Conciousness is always preserved, and in two cases attacks were preceded by ocular motor disturbances (skew deviation, nystagmoid jerks and conjugate deviations). Exceptionally, the transient hemiparesis may be preceded by a grand mal epileptic fit, though they are more likely to appear sporadically and independently of the paretic changes. In the interparoxysmal periods the children showed pronounced hypotonia, hyperkinetic extrapyramidal features and oligophrenia. Neuroradiological procedures have excluded brain anomalies of vascular or other aetiology and simple biochemical analyses were negative. EMG during paretic periods have revealed central motor neuron lesions, while EEG demonstrated non-specific paroxysmal features. A brain-stem dysfunction in the aetiology is postulated.