Eleven patients with acute myeloblastic leukaemia have received repeated intravenous injections of BCG containing 4-9 X 10(6) live organisms per millilitre. Non-caseating epithelioid granulomas, sometimes with giant-cell formation, have been demonstrated in eight bone marrow aspirates. Seven patients had granulomas in the liver, three in the lung, one in the spleen, one in lymph nodes, and one in a skin biopsy. One patient had a raised serum alkaline phosphatase, but none of the patients had any illness which could be related to the presence of granulomas. Granuloma formation appeared more extensive in four patients who were probably anergic before BCG treatment. Until the significance of this finding becomes clear great care should be taken when giving BCG by the intratumour of intravenous routes to potentially immunoincompetent patients.