1. Fifteen kittens were monocularly deprived of vision by suturing the lids of the right eye together for various periods of time at different ages. A simple behavioural technique was used to assess the immediate effects of the period of monocular deprivation on the visual acuity of the deprived eye as well as the time course of any subsequent recovery.2. The extent of the recovery of vision was measured under conditions where the animal was either forced to use its deprived eye by performing a reverse suture or where the animal had both eyes open after the initial period of monocular occlusion.3. The initial effects of monocular deprivation were graded in severity according to the age at which the deprivation was imposed, ranging from apparent blindness in animals deprived at 6 weeks of age to only a small loss of acuity in kittens deprived at 12 weeks of age.4. The effects of deprivation imposed from birth were particularly severe, leading to a temporary blindness. Nevertheless after a period of time that became progressively longer with increasing deprivation, all animals showed some recovery of pattern vision over the course of the next 2 or 3 months. The extent of this recovery became progressively less as the period of deprivation was prolonged. There was even some recovery of vision (an acuity of 2.5 cycles/deg) in animals that were deprived throughout the duration of the ;critical period' to 4 months of age.5. Direct comparison of the rate of behavioural recovery between animals that were reverse sutured with that of litter-mates that received binocular input after monocular occlusion to either 45 or 60 days of age proved to be remarkably similar, although the acuity that was eventually attained by the reverse sutured animals was always slightly higher.6. The recoveries observed after reverse suturing were reasonably well correlated with changes observed in the ocular dominance of visual cortical cells under similar circumstances.7. Although the recovery in these animals can be accounted for by the simple notion of a competitive interaction between the two eyes, the recovery observed in animals that had both eyes open after the initial period of deprivation cannot be so readily explained. Evidently there must be an additional non-competitive mechanism of recovery.