All of the recombinant interferons are active agents for the systemic treatment of mycosis fungoides and Sézary syndrome. The response rates are similar to those observed with systemic chemotherapy. There is no clear evidence that combining interferons with other systemic therapies increases the response rates. The combination of interferon with PUVA provides provocative results. The optimal role of interferons in the treatment of mycosis fungoides and Sézary's syndrome is undefined.