['To assess the role of granulocyte colony-stimulating factor (G-CSF) in autoimmune neutropenia (AIN).', 'Serum G-CSF levels were measured in 57 children with AIN. Two different G-CSF-dependent assays were used: a solid-phase "sandwich" enzyme-linked immunosorbent assay and a proliferation assay. Sera from healthy persons and from patients with severe congenital neutropenia were used for negative and positive controls.', 'The median G-CSF level in healthy persons (n = 13) was low, 45.6 pg/mL (range <39 to 141 pg/mL). The median G-CSF level in patients with AIN (n = 57) was very similar, 45.5 pg/mL (range <39 to 2500 pg/mL). Forty-five (79%) of 57 patients with AIN had levels within the range of the control group. Seven (12%) had marginally increased G-CSF levels (141 to 400 pg/mL), and only 5 (9%) had levels higher than 400 pg/mL. The G-CSF levels measured by enzyme-linked immunosorbent assay correlated well with levels measured by the proliferation assay, thus demonstrating that antibodies present in patient sera did not affect the biologic activity of G-CSF.'] Are serum granulocyte colony-stimulating factor levels increased in patients with autoimmune neutropenia of infancy?