Preleukemic cells could be detected in the bone marrow cell population of SJL/J mice within several days after induction of leukemia by repeated feedings with a chemical carcinogen 7,12‐dimethylbenz[a]anthracene (DMBA). Bone marrow cells collected 7,30 or 60 days following carcinogenic treatment, developed lymphoid tumors upon transplantation into syngeneic irradiated recipients. The incidence of these tumors varied between 40–45 % when the bone marrow cells were collected and transferred 7–30 days after feeding with DMBA, and raised to an incidence of 80 % when transferred 60 days after carcinogen administration (compared to 50 % incidence in the DMBA‐treated bone marrow donors). A survey of several cell surface components on the lymphoid tumor cells, obtained after transplantation of preleukemic cells, indicated that most of the tumor lines bore both the Thy‐1.2 antigen (weak) and the Fc receptor, whereas the rest were positive only for the Fc receptor. None of these tumor cell lines would yield a significant amount of cell‐bound immunoglobulin.