We read with interest the article on a positive association between a polymorphism in the tryptophan hydroxylase (TPH) gene and manic-depressive illness.1 The authors found a significantly increased rate of the "A" allele in patients compared with control subjects (52% vs 36%).1 The TPH gene encodes for the rate-limiting enzyme of serotonin synthesis, making it a strong candidate gene for manic-depressive disorder; therefore, we attempted to replicate these results.