Monocular optokinetic nystagmus (OKN) was studied in 24 human infants aged 3-35 weeks using electro-oculography and moving vertical gratings. At a constant velocity of 25 deg/sec, infants display direction dependent slow phase asymmetries until approximately 5 months after birth. A comparison was made of the cumulative eye displacement during the slow phases of OKN for nasal and temporal movement.