Work is in progress on genetic polymorphisms of glutathione S-transferase and cytochrome P-450, enzymes involved in organochlorine compound biotransformation, to explore the gene–environment interactions as a possible cause of the observed higher levels of the aforesaid compounds in patients with endometriosis and as a risk factor for the disease onset/progression, as suggested by some studies (Ertunc et al. 2005; Hsieh et al. 2004; Tsuchiya et al. 2007). Here, CYP4F3 is linked to endometriosis.