SV40 antigen was detected on sections through malignant oromaxillofacial tumors in 47.8% of the cases, with a higher incidence among the epithelium originating tumors. Anti-SV40 CF antibodies were detected in 83.6% of the examined subjects with cancer, but only in 57.9% of the blood donors. The titers were quite low in general. The results are discussed from the point of view of the immunologic status of the patients.