Antigens of viral tumours are the same for all the tumours due to the same virus. Antibodies in tumours bearing animals allow to detect antigens in nucleus, in cytoplasm and on the cell membrane which carries also embryonic antigens and the antigen responsible for tumour rejection by sensitized lymphcytes (TSTA or TATA). Is this antigen identical to the surface antigen shown by antibodies? Purification of membrane antigens will answer this important question. Chemically induced tumours bear tumour rejection antigens having an individual specificity, perhaps related to modified histocompatibility antigens, and embryonic antigens. Both give rise to antibodies and sensitized lymphocytes. Among human tumours, Burkitt lymphoma is strongly antigenic. Its viral origin is highly likely. Antibodies in sera of Burkitt patients react with antigens present in nucleus, cytoplasm and on the membrane of malignant or transformed cells. Sensitized lymphocytes in the peripheral blood recognize a membrane antigen probably different of that revealed by antibodies. Antibodies found in sera of patients with carcinoma react mainly with tissular antigens. In these cases, methods exploring delayed type reactivity, such as leukocyte migration inhibition and moreover skin testing with tumour extracts, gave some promising results.