Until quite recently. pharmacogenetic polymorphisms in oxidative drug metabolism were considered rare. However during the last years several monogenically determined poly of oxidative reactions in drug metabolism involving benzylic hydroxylation of debrisoquine, N-oxidation qf sparteine, C-hydroxylation qf tolbutamide, O-de-ethylation of phenacetin, phydroxylation qf phenytoin and mephenytoin and N-glucosidation of amylobarbitone (amobarbital) have been discovered. The incidence qf these various pharmacogenetic conditions varies between 2 and 9 % of the population. Among these conditions the best studied examples are the polymorphic oxidation qf debrisoquine and sparteine.