A young man with severe psoriasis was treated intermittently with methotrexate. On two different occasions, severe oligospermia documented by serial seminal fluid analyses was present coincident with methotrexate administration. Discontinuation of methotrexate resulted in normal sperm concentration. Measurements of serum gonadotrophin and testosterone levels were normal during and after methotrexate treatment. It is concluded that methotrexate administration may result in severe oligospermia and that these inhibiting effects on spermatogenesis are reversible.