Between June 1982 and March 1983, 11 patients with aggressive recurrent respiratory papillomatosis were treated with alpha or human leukocyte interferon (IFN) that was produced by and purchased from the New York Blood Center, Inc. The year before, nine of these patients had been on a similar protocol utilizing alpha-IFN that had been supplied by the Finnish Red Cross Blood Transfusion Service. Comparisons regarding response and toxicity were made and are reported. In our series we have not seen an overall difference in response of papillomatosis to these two IFNs. As many of our patients responded better to the New York product as responded worse. There is a suggestion, however, that the New York product is associated with less toxicity than the Finnish IFN.