Cats were submitted to repeated step stimulations either vestibular or optokinetic. Regardless of which of the two stimuli was used, dynamic modifications were observed in both vestibulo-ocular response and optokinetic after-nystagmus (OKAN). The progressive changes in post-rotational nystagmus and OKAN were quantified by measuring the duration of their primary phase. A parallel evolution of these two parameters was found. When repeated unidirectional vestibular stimulations were used, the same asymmetry was induced in both vestibuloocular responses and OKAN. These results support the hypothesis that the vestibulo-ocular and the optokinetic reflex share a common velocity storage mechanism, although alternative hypotheses cannot be excluded.