Totally 161 basal cell and squamous cell carcinoma (BCC, SCC) patients were treated with human natural leucocytic interferon (HNLI) and recombinant IFN alpha 2c. After HNLI treatment, 61 out of 86 BCC patients and 29 out of 45 SCC patients were cured according to histopathologic and clinical findings. In 13 BCC and 13 SCC patients, the cancer lesion was reduced 25%-90%. After recombinant IFN alpha 2c treatment, 14 of 20 BCC patients and 4 of 10 SCC patients were cured according to histopathologic and clinical findings. In 6 BCC patients and 5 SCC patients the cancer lesion was reduced 25% to 90%. Both types of interferons are effective in the treatment of BCC and SCC patients. Local application of interferon stimulates immune reaction at the site of the tumor. There is a marked difference between the spontaneous macrophage activity and that induced by interferon. The interferon activated macrophages are significantly larger, the number of lysosomes and the density of macrophages is increased. In difficult locations intralesional therapy can be considered to avoid disfigurement of the patients with or without surgery.