The period of susceptibility of the visual cortex of kittens to the effect of squint is limited to the first three postnatal months. The reduction of binocularity found in these kittens as reflected by the distribution of neurons according to their ocular dominance is especially emphasized in animals operated on between the ages of 4-7 weeks in comparison to animals operated on between the ages of 8-11 weeks. The proportion of monocularly dominated neurons within the first three postnatal months is significantly (0.05 greater than p greater than 0.025) reduced with age. Similar effect on cortical neurons was found for animals who were under the influence of squint for 6 weeks or 15 months and for animals with wide range of deviation angles.