Over 6 1/2 years, 182 patients with acute myelogenous leukaemia were treated with one of two combinations of chemotherapy containing cytosine arabinoside and an anthracycline (daunorubicin or doxorubicin). Eighty-one patients achieved remission and 79 of them were entered into one of two trials of active immunotherapy. The first trial compared maintenance chemotherapy and i.v. BCG immunotherapy with chemotherapy alone. The results have shown that the group given i.v. BCG survived for a significantly longer time (P = 0.035) than the group treated only with chemotherapy. The i.v. BCG treated group also had a significantly longer survival (P = 0.042) after their first relapse and a higher incidence of subsequent remissions. However, there was no difference in the length of first remissions for the two groups. The second trial compared two different types of active immunotherapy. The results show no significant difference in remission duration or survival after first relapse for 34 patients randomly allocated to treatment with i.v. BCG or irradiated leukaemic blast cells. Sixteen patients relapsed and subsequently 10 patients entered a second remission after reinduction chemotherapy. These patients were distributed evenly between the two immunotherapy groups and this high rate of second remissions is similar to that for the immunotherapy group in the first Cardiff Trial. In the two trials, 21 (62%) of 34 patients receiving immunotherapy entered a second remission after reinduction chemotherapy and six patients achieved third remissions.