Brain electrical activity mapping (BEAM) allows the study of electrical visual reactivity on a computerized electroencephalogram (EEG). We carried out 150 BEAM studies on 120 infants to evaluate the usefulness and reliability of this noninvasive technique in the assessment of vision in very young children, compared with other methods (clinical testing, preferential looking, and visual evoked potentials). BEAM demonstrated amblyopia at a cortical level and showed specific electrical signs of amblyopia. The visual reactivity was variably affected depending on the type of amblyopia present. In addition, different results of BEAM corresponded to different kinds of visual maturation delay and strabismus in the absence of amblyopia. BEAM appears to be useful in the initial screening and during treatment of deprivation and strabismic amblyopia, especially when other methods have failed to elicit the level of vision.