The involvement of vitamin C and conditional B vitamins, e.g., niacin, biotin, pantothenic acid, choline and inositol in human nutrition and disease is discussed. The symptoms of common B vitamin deficiencies are described including pellagra, Leiner''s disease, burning feet syndrome and reportedly associated with malnutrition, starvation, alcoholism and burns. The metabolic bases of vitamin B related inborn errors are explained for cases of Hartnup''s disease, propionic acidemia and .beta.-methylcrotonylglycinuria.