A number of studies have shown that drug glucosidation occurs in vertebrates. This review summarizes information on the chemical, physical and biological properties of eleven drug glucosides. Three out of two hundred individuals exhibited a complete lack of amobarbital-N-glucoside formation. The data from a pair of identical twins who were deficient in this metabolic pathway suggested the presence of a recessive trait controlled by a single pair of autosomal genes which regulate N-glucoside formation. In addition, average values seemed to be subject to interethnic variation.