A series of 12 vegans have been investigated clinically from the aspect of vitamin-B} 2 metabolism and deficiency. It is suggested that their comparative freedom from manifest signs and symptoms in the central nervous system is due to their having the major portion of their low serum vitamin B12 in the hydroxo form. A comparison is made betweenveganism andtobacco amblyopia, and attention is drawn to cyanide metabolism. The possibility of endogenous and exogenous factors interfering with this and producing subsequent demyelination is discussed. Although most of these subjects were clinically normal, the electroencephalographic evidence suggests that occult damage to the central nervous system is taking place and that this form of diet may produce subtle cerebralchanges that are unrecognizable by normal clinical methods.

I am grateful to Professor A. Kekwick and the members of the ClinicalResearch Committee, Instituteof Clinical Research, Middlesex Hospital Medical School, for providing me withfacilities to conduct much of this work. It was produced during the tenure of a Leverhulme Research Scholarship and a grantfrom the North-west Metropolitan Regional Board. I also thank my sponsors, Dr. Michael Kremer and Dr. RJ Porter, for their continued advice and encouragement. Dr. George Discombe and Dr. CC Evans gave me considerable help with the haematological and electroencephalographic investigations, which proved invaluable in the assessment of these subjects. Finally, Dr. Frank Wokes enlisted the help of thevegan volunteers and gave me freely of his wide knowledge and advice.