A total of 88 better risk patients and 47 poor-risk patients with chronic myeloid leukemia have received repeated vaccinations with BCG or BCG-cultured cell mixtures at our institutions. The number of viable BCG organisms injected appeared to be the most important parameter of immunologic stimulation in this study. Excessive doses of BCG were associated with a significant incidence of disabling complications and with no survival benefit. Better risk patients receiving lower doses of BCG had suggestive prolongation of survival (p less than 0.1). Immunotherapy had little effect on the course of poor-risk patients but evaluation of this heterogeneous population is difficult; additional studies would be desirable among patients in whom reversal of poor prognostic signs can be achieved.