In a 2-year period, 37 of 81 adults with acute myelogenous leukaemia achieved complete remission after repeated courses of Daunorubicin (DNR) and Cytosine Arabinoside (ARAC). They were randomized to maintenance treatment with monthly DNR/ARAC, or to identical chemotherapy plus intravenous BCG. Eighteen BCG treated patients had significantly longer survival times than 19 patients treated with chemotherapy only although no statistically significant difference can be seen in the remission duration of the two groups. Eleven patients in the BCG treated group who have relapsed, have received DNR/ARAC reinduction and five second and two third remissions have been obtained. Twelve control group patients have relapsed and 10 have received further reinduction treatment with DNR/ARAC but only one patient has entered a complete remission. Seven patients in the BCG treated group who survived for 75 weeks or more (76, 76, 96, 124, 125, 138 and 145 weeks) were either PPD positive before treatment or converted to PPD positivity after BCG treatment. Using a battery of skin tests it may be possible to define a good prognostic group of patients and design future treatment accordingly. The BCG group had a total of 198 intravenous treatments. All patients had pyrexia 6-12 h after injection lasting 12-72 h and occasionally headaches and muscle pains. Two patients had non-fatal anaphylactic reactions which did not recur when BCG was subsequently re-administered. Other complications of BCG therapy were not a problem and we have not needed to withdraw treatment for any patient.