We describe an Ii-year-old boy with acute Q fever complicated by hemop
hagocytosis. In addition to pancytopenia, the boy presented with hypon
atremia, hypofibrinogenemia, and changes in lipid metabolism. Examinat
ion of a bone marrow aspirate revealed striking hemophagocytosis. All
of the pathological changes were caused by an activated macrophage sys
tem. We also discuss the possible role that pathogenetic mechanisms pl
ay in these changes.