A purified antigen from human acute myelogenous leukemia (AML) cells has been used to produce a myelogenous leukemia-associated monoclonal antibody. In limited FACS-IV analyses the monoclonal antibody to leukemia (CAMAL-1) as well as a conventional rabbit antiserum have been used to positively identify AML or chronic granulocytic leukemia patient cell samples. Neither CAMAL-1 nor the rabbit antiserum bound appreciably to acute lymphocytic leukemia cells, normal bone marrow, or normal peripheral blood leukocytes. CAMAL-1 was shown to be specific for AML cell extracts in the ELISA and was successfully used as an immunoadsorbent for the purification of the AML antigen from cell extracts. No significant levels of equivalent antigen were found when cell extracts from normal cells, lymphocytic leukemia cells, and lymphoma cells were similarly absorbed. These findings indicate that CAMAL-1 shows considerable specificity for an antigen associated with cells from patients with myelogenous leukemia.