A 19-year-old girl developed a fever of up to 40 degrees C and, during an episode of high fever, generalized seizures. Physical examination on admission was unremarkable, except for several small lymph nodes. Differential blood count showed a leukopenia (1700/microliters) with 14% stab and 7% segmented neutrophils. After initial clinical improvement she again became feverish and the differential count now showed agranulocytosis with a total white cell count of 1400/microliters. Because of the time of year and the geographic location borreliosis was now considered in the differential diagnosis. The antibody titre against Borrelia was raised to 1:64 (IgM) and 1:256 (IgG). Her condition and the differential blood count rapidly improved on intravenous antibiotic treatment with cefotiam (2 g two times daily) and gentamicin (120 mg two times daily), as well as filgrastim (granulocyte-colony stimulating factor) subcutaneously. Antibiotic treatment was continued after 6 days with oral ampicillin (1 g three times daily) for 3 weeks. Follow-up examination six weeks later found the patient to be symptom-free.