We adopted the estimate of the intraclass coefficient of reliability, R, to evaluate the reliability of smooth pursuit eye movement quantitative analysis. At a one-week interval, we recorded twice smooth pursuit eye movements from fifteen healthy subjects by means of the binocular electrooculographic technique. R was computed for the constant and the slope of the target velocity/gain relationships. R values were rated good for the slope and excellent for the constant. Finally, we computed for each parameter the maximum variability value according to two differing methods; on the basis of the within-subjects mean square values, we defined the normal range of biological test-retest variability for the two parameters.