Summary. We present the results of the immunohaematological tests performed in an unselected group of patients with acute leukaemia at the time of diagnosis, and when possible the follow‐up in remission and/or in relapse. Thirteen out of the 112 patients tested had a positive Coombs test at the time of diagnosis and, in six patients, the Coombs test became positive during remission. All the 19 positive Coombs test were of the complement type with, in 11 cases, an anti‐I antibody eluted from the patient's RBC. There was no relationship between the FAB morphologic subtype, the presence of other immune abnormalities, the course of the leukaemia and the immunohaematological abnormalities. Several hypotheses on the possible relationships between the acute leukaemias and the immunohaematological abnormalities are discussed.