Ticlopidine is increasingly used in the secondary prophylaxis in patients with arterial occlusive diseases. Neutropenia is a well known side effect of this drug. We report a case of a 73 year old woman who was admitted because of severe prolonged ticlopidine induced leucopenia. The past medical history included an immunocytoma of the IgM-kappa type diagnosed seven years ago with less than 10% infiltration of the bone marrow and a chronic hepatitis C. On admission the white cell count was 1000/microL. Ticlopidine was stopped. The white cell count did not increase within one week, thus filgastrim was applied on two consecutive days. The leucocyte count promptly increased to 6000/microL but consecutively dropped within the next fortnight again to levels below 500/microL forcing daily filgastrim application for another 9 days. Four months after the initiation of the therapy with filgastrim the patient had a white cell count of 4300/microL. We therefore conclude that in patients with a history of potentially bone marrow suppressing diseases the use of ticlopidine has to be carefully weighed against possible myelosuppressive effects.