Neutropenia is an occasional complication of treatment with cephalosporin antibiotics. This report describes two patients who had neutropenia while receiving high doses of cephalosporins. The neutrophil counts returned to normal after stopping the drug, and cephalosporin-dependent neutrophil antibodies were demonstrated in both cases, using the granulocyte immunofluorescence test. In one patient, the immune neutropenia appeared to be due to a drug adsorption mechanism similar to penicillin-induced haemolytic anaemia, while an immune complex mechanism may have been involved in the second patient.