Very few data on the frequency and diversity of haematological abnormalities occurring in brucellosis in children have been reported. In the present study 110 children (56 boys and 54 girls; age range, 2 months to 14 years) with proven brucellosis were investigated to determine the haematological changes during the active course of this infection. Anaemia was detected in 48 (44%) patients, of whom four had evidence of haemolysis. Leukopenia occurred in 33% of the cases, with neutropenia and/or lymphopenia being the most striking features encountered. Thrombocytopenia was found in six (5%) patients and pancytopenia in 15 (14%) patients, of whom one developed disseminated intravascular coagulation. Clinically detectable bleeding occurred in five (4.5%) patients whose platelet counts were significantly low. Hypersplenism, haemophagocytosis and granulomatous lesions of the bone marrow appear to play a fundamental role in producing these abnormalities of the peripheral blood. Brucellosis may be considered in patients whose blood picture reveals haemolytic anaemia, leukopenia, thrombocytopenia or pancytopenia, particularly when the disease is epidemiologically suspected.