Cytochrome P450 CYP2D6 polymorphism is an autosomal recessive trait leading to impaired sparteine/ debrisoquine metabolism in 5-10% of the Caucasian population. Previous studies have associated affected individuals (poor metabolizers = PM) with susceptibility to bladder cancer and various forms of leukemia. In many other cancer forms, the data remain contradictory. A PCR assay allows the convenient screening of about 90% of known mutations resulting in the PM phenotype. Since in patients with neurofibromatosis type 2, we had observed a significantly increased rate of CYP2D6 mutations leading to PM and apparently predisposing for NF2, we extended our investigation to tumor and peripheral blood samples obtained from NF1 patients. Although the number of cases investigated remains low, the study indicated that during tumor formation no changes occurred at the mutational hot spot within the CYP2D6 sequence. Moreover, no loss of heterozygosity was notable. However, the frequency of the mutated allele in the NF1 individuals is comparable to that of neurofibromatosis type 2 and above that observed in breast and colon cancer, or meningiomas.