Armstrong, Donald (Children's Hospital of Philadelphia, Philadelphia, Pa.), Gertrude Henle, and Werner Henle. Complement-fixation tests with cell lines derived from Burkitt's lymphoma and acute leukemias. J. Bacteriol. 91:1257-1262. 1966.-Cells of various lines isolated from Burkitt's lymphomas and acute leukemias and disintegrated by freezing and thawing or sonic treatment were found to react in complement-fixation tests with a considerable proportion of human sera. At least 10(7) cells per milliliter were required for antigenic activity. All but one of 13 sera from Burkitt lymphoma patients were positive, with titers ranging from 1:8 to 1:320. About 20% of sera from American children and 60% of sera from adults, regardless of diagnosis, showed titers in a similar range. Sera giving positive tests with one of the neoplastic white cell antigens usually reacted also with many if not all of the others, but rarely with antigens derived from normal peripheral leukocyte cultures and not at all with HeLa or other human nonleukocytic cells. Various observations indicate that the complement-fixation test measures mainly antigens which are different from those detected by immunofluorescence. The nature of the reactions described remains obscure.