We report the identification of a novel and defective variant of the gene encoding cytochrome P450 2D6 (CYP2D6). This novel variant is a subtype of CYP2D6*6 that was undetected by a commercially available 5' exonuclease-based assay. Because the novel variant was found in only one of 609 individuals, it represents a rare subtype of CYP2D6*6 that may be restricted to a single family or a subpopulation. A procedure for the identification of the novel CYP2D6*6 variant using restriction enzyme treatment of amplified fragments was developed.