A case of severe immune haemolytic anaemia in a 54-year-old man suffering from Mycoplasma pneumonia is presented. A strongly positive direct Coombs test with erythrocyte bound IgG, C3d and C4 was demonstrated during the haemolytic process. Further, serologic investigations revealed ampicillin-dependent 'warm' antibodies and a cold agglutinin titre greater than 2000. No firm conclusion can be drawn as to which antibody caused the haemolysis. Treatment including withdrawal of antibiotics, blood transfusions (washed red cells, concentrated erythrocyte suspension) and corticosteroids was successful. It is suggested that tests should be carried out for erythrocyte bound drug-induced antibodies in cases of haemolysis with a history of drug exposure.