267 amblyopia similar to tobacco amblyopia occurring as a result of malnourishment only, without any intake of tobacco. He also maintained that chronic, sustained, low-level cyanide intoxication, an experimental situation similar to that produced by smoking, does not cause any neurological effects. He has also challenged the exclusive role of B1,, pointing out that deficiency of vitamins other than B1, can cause a tobacco-amblyopia-like syndrome which can be cured by an adequate diet supplemented by brewer's yeast. Also, Calhoun (1918) described similar paracentral as well as central scotomata in patients with pellegra which could be cured by the administration of nicotinic acid. Some claim has also been made for riboflavin deficiency as a factor in such amblyopias. While deficiency of vitamin B,, may play a part in the causation of tobacco amblyopia, it is likely that other B vitamins and perhaps other nutritional factors produce the same pathological effect.Whereas we found striking improvement with hydroxocobalamin in many of our cases, equal improvement was seen in others with cyanocobalamin, corticotrophin, or prednisolone, or spontaneously. Spontaneous recovery in optic neuritis is well known (Traquair, 1957;Walsh, 1957). Of the three patients with bilateral centrocaecal scotomata simulating tobacco amblyopia, one improved on corticotrophin alone, while another started improving spontaneously before hydroxocobalamin was given.Hence two conclusions can justifiably be drawn from our cases.(1) That tobacco amblyopia is rare in this part of India in spite of a large population of vegetarian smokers. This is the more interesting in view of the fact that in the control series vegetarian smokers had high plasma thiocyanate levels and the lowest serum B1, levels in the population. (2) That smoking, vegetarianism, and vitamin B1, (either as hydroxocobalamin or as cyanocobalamin) play no part in the pathogenesis of isolated "idiopathic" optic neuritis as seen in our patients.We are grateful for a grant from Glaxo Laboratories (India) Ltd., and for grant No. 01-011-1 from the National Institute of Health of t-he U.S. Department of Health, Education, and Welfare.