The influence of 2-chlorodeoxyadenosine (2-CDA) administered alone and in combination with cyclophosphamide (CY) or methotrexate (MTX) on the survival time of mice bearing L1210 or P388 leukemia was investigated. 2-CDA given alone significantly prolonged survival time of mice bearing L1210 leukemia and caused only a slight prolongation of survival time in mice bearing P388 leukemia. Survival times of mice bearing both kinds of leukemia, receiving combined therapy of 2-CDA and MTX were not significantly prolonged as compared with mice treated with these agents separately. The groups of mice with both leukemia L1210 and P388 treated with 2-CDA and CY lived significantly longer as compared with the control group and with mice receiving only single cytostatic.