This protocol was conducted to demonstrate whether a folic acid supplement (7 mg or 38.5 mg/week) would reduce methotrexate toxicity in patients with psoriasis while preserving the efficacy of the drug. In addition, we attempted to demonstrate that urinary levels of aminoimidazole carboxamide (AIDA), adenosine (Ado), and dexoyadenosine (dAdo) are elevated in methotrexate-treated patients with psoriasis compared to controls. AICA, Ado, and dAdo are known to be immunotoxic substances and they may be the link between methotrexate therapy, immunosuppression and efficacy in psoriasis therapy. This study has been concluded and we are currently analyzing data.