Human natural leukocytic interferon (HNLI) and recombinant interferon (rIFN) alpha 2c can be used in the therapy of basal cell carcinoma. Seventy-two patients were treated for 3 to 6 weeks with a single dose of 400,000 to 1,200,000 units (HNLI) and 2,000,000 to 5,000,000 units (rIFN alpha 2c). According to histopathologic and clinical findings, 52 patients were cured, and cancer cells were not found in the biopsy material taken after HNLI treatment for the second biopsy. In nine of 72 patients the cancer lesion was reduced 25% to 90%. In 11 patients it was not reduced or was reduced less than 25%. With rIFN alpha 2c therapy given five times per week for 4 weeks, histopathologic and clinical findings showed that five patients out of 12 were cured, and cancer cells were not found in the biopsy material taken after treatment. In seven patients out of 12 the cancer lesion was reduced 25% to 90%. Both types of interferons are effective in the treatment of basal cell carcinoma. Side effects were mild.