Objective: To investigate the effect of Narrow Band Ultraviolet Photo Therapy On Serum Homo-cysteine Levels in Patients Refered to Yahyanegad Hospital Of Babol. Design:(Study group: patients with dermatological disorders including psoriasis, vitiligo or atopic dermatitis that are referred to photo therapy unit at Yahyanegad hospital; Sample size:30; No control group; Building: Not blinded; Randomization: Single arm study). Setting and conduct: 30 patients that are referred to photo therapy unit of the dermatology department at Yahyanegad hospital are enrolled in to the study. Serum homocysteine levels are measured in all patients at the first visit before initiating of treatment and after thirty sessions of treatment. Serum homo cysteine levels are determined using Elisa method. Software SPSS are used to analyze the results. Inclusion criteria: psoriasis or Vitiligo, which is set to be at least 30 sessions of narrow band ultraviolet photo therapy. Signing the informed consent before entering the examination Exclusion criteria: Smoking, illnesses such as hypertension, diabetes, thyroid dysfunction that may affect homocysteine levels. Use of drugs, such as vitamins, OCP and anti-coagulant, past history of cardiovascular, chronic hepatitis, chronic kidney disease, cancer and pregnancy, inflammatory bowel disease, rheumatic diseases, systemic drugs anti-psoriasis or Vitiligo, Use of natural or synthetic UV for during the months prior to admission natural or synthetic. Patients who did not complete therapy by the end of 30 sessions. Intervention: Narrow Band Ultra Violet B photo therapy; thirty session of treatment. Primary outcome variables: serum homocysteine levels; Secondary outcome variable Ultraviolet cumulative doses