The acute effect of a moderate quantity of alcohol on balance was examined by the pendular optokinetic nystagmus test (P-OKN test), pendular rotation test (VOR test), caloric test and dynamic posturography (EquiTest). Ten healthy male volunteers aged 19-27 (avg. 22.8) years were given 1.5 ml whiskey (alcohol content 43%) per kilogram of body weight within 5 minutes. Their blood alcohol level (BAL) was measured before administration and 30, 90, and 150 minutes later.Equilibrium examinations were performed immediately after each blood sample was taken. At the highest alcohol level, in P-OKN gain, VOR gain, maximum slow phase velocity of the caloric test and equilibrium score of the sensory organization test in conditions 4 and 5 were significantly lower than before drinking. In some typical cases, the subjects' responses to all tests were most disturbed at the time of the highest alcohol level.Our results indicate that a moderate quantity of alcohol affects not only the oculomotor system but also the vestibular system. Furthermore, it may be that one of the reasons for postural instability after drinking alcohol is reduced vestibular function.