In seven recently diagnosed and untreated patients with tobacco amblyopia the light and dark adapted electroretionograms were recorded together with visual acuity, central fields and the Farnsworth-Munsell 100-Hue test. After 3 months treatment with injections of hydroxocobalamin all these tests were repeated. An improvement in visual acuity resulted in all cases. A significant reduction in the Farnsworth-Munsell total error score of the seven patients was noted (p less than 0.01). A significant increase in the amplitude of the light adapted b-wave of the ERG was found (0.01 less than p less than 0.02) following the course of hydroxocobalamin injections. No other significant changes in the ERG were demonstrated. It is suggested that the ERG changes demonstrated an improvement in an abnormal biochemical state in those bipolar and perhaps Müller cell of the inner nuclear layer of the retina which make electrophysiological connnections chiefly with foveal cones.