Time-concentration curves of recombinant human interferon alpha$(rIFN-{alpha}A)$ in the skin and serum of nude mice or rats were studied after topical application of IFN ointment. IFN appeared in the skin and serum in less than 30 minutes and lasted for more than 10-12 hours at high concentration level after the application to nude mice at a dose of $9.0{ imes}10^5;IU/g$ mouse. But in the rats, IFN was not detected in the serum even 7 hours after the application at a dose of $6.0{ imes}10^5;IU/g$ rat. Topical application of IFN might be useful for the topical and systemic treatment if the human skin resembles that of nude mouse in respect to transport characteristics.