Continuous monocular deprivation (MD) during early postnatal life results in reduced cortical representation and visual acuity of the deprived eye. However, loss of visual function in one eye after just a brief period of compromised vision would appear to be maladaptive. The extent to which MD effects can be counteracted by balancing periods of MD with those of binocular exposure (BE) has not yet been established. We therefore reared young cats with a daily regimen in which they received variable amounts of MD (by wearing a mask) and BE for about 3 weeks, and subsequently assessed the functional architecture of visual cortex with optical imaging of intrinsic signals, followed by visually evoked potential and single cell recordings. Anaesthesia was induced with an i.m. injection of ketamine (20-40 mg/kg) and xylazine (2-4 mg/kg). Following tracheal cannulation, animals were artificially ventilated and anaesthetized with a mixture of N₂O (55-65%), O₂ (35-45%) and isoflurane (2-2.5% during surgery, 1-1.5% during recording). During recording neromuscular blockade was maintained with a continuous i.v. infusion of gallamine triethiodide (10 mg/kg/h) in glucose-saline. ECG and EEG were constantly recorded to monitor the state of anaesthesia. In a first group of animals with 7 h of overall daily visual experience, only 2 h of BE allowed normal ocular dominance architecture to develop despite 5 h of MD, with the deprived eye occupying 46.1 ± 4.4% (mean ± sem, n = 3) of the cortical surface. Even the results for 1 h (42.1 ± 3.2%, n = 4) and 0.5 h BE (39.6 ± 2.0%, n = 3) were close to normal (48.9 ± 4.0%, n = 4). A second group of cats received mixed visual inputs for just 3.5 h a day. We again found that subjects with binocular experience of 0.5 h a day or more exhibited close to normal ocular dominance architecture, while for 0.25 h of BE the cortical representation of the deprived eye (24.0 ± 2.8%, n = 5) was significantly reduced in terms of territory occupied (1-way ANOVA, P < 0.01). The relationship between the effects of deprivation and daily BE was similar regardless of the length of overall visual experience. When a 0.5 h BE period was broken up into two blocks of 0.25 h BE flanking the MD period, ocular dominance (deprived eye, 26.0 ± 3.6%, n = 6) resembled that of animals that had received only 0.25 h BE, suggesting that binocular experience must be continuous to be most effective. Our results demonstrate that periods of normal experience are more efficacious in driving visual cortical development than those of abnormal experience, and that it is the absolute duration of binocular exposure and not the relative ratio of BE vs. MD that determines the outcome.