Methotrexate is used for psoriasis by the majority of teaching services of dermatology in the United States. Three modes of administration were compared: small daily doses by mouth in interrupted schedules, single large weekly oral doses, and parenteral doses. All methods were effective and had toxicity, but the parenteral route showed the greatest toxicity. The drug is contraindicated in pregnancy, hematological disorders, peptic ulceration, and liver disease. Chromosomal breaks have been reported with greater frequency than normal. Renal clearance is vital. The drug should be considered only for very severe forms of psoriasis.