Three patients were analysed for an extreme leucocytosis (>50 x 10<sup>9</sup>/l) because leukaemia was suspected. In all three patients the leucocytosis proved to be caused by a leukaemoid reaction. This reaction was associated with a hepatic angiosarcoma in the first patient, with a Salmonella infection in the second patient and with a necrotic leg abscess in the third patient. Retrospectively, 25 patients with a leukaemoid reaction were identified in our hospital during a four-year period. Besides leukaemia, a leukaemoid reaction, which often has a dismal prognosis, should be considered in patients with an extreme leucocytosis.