Antisera against five newly established AKR spontaneous leukemias (KSL) prepared by immunization of KSL cells in (C57B1/6 X C3Hf/He)F1 mice were preabsorbed with non-leukemic AKR lymphoid cells to remove antibodies against virus-associated surface antigens and alloantigens. In absorption tests the antisera showed no cross-reaction by immunofluorescence microscopy with thymocyte, fetal, male-specific H-Y, E and X.1 antigens; with known Gross murine leukemia virus-associated antigens; or with cell surface antigens on Friend, Moloney and Rauscher virus-induced tumors. It was thus shown that the antigens detected were leukemia-specific, were acquired by malignant transformation, and consisted of two types: (1) a common antigen in all the KSL, and (2) individual antigens found in four of the KSL which showed distinct patterns of partial cross-reactivity with the other KSL.