A primary abnormality of leucocyte function—a deficiency of chemotaxis— has been found in two unrelated children with recurrent infection. The syndrome is characterised by recurrent stomatitis, otitis, gingivitis, and low-grade fevers, normal humoral and cellular immunity, severe peripheral neutropenia, normal numbers of mature, morphologically normal neutrophils in the bone-marrow, poor peripheral blood leucocyte response to chemical or inflammatory stimulation, poor neutrophil chemotaxis, and severely impaired random mobility of neutrophils. Neutrophils from peripheral blood or from bone-marrow suspensions had normal phagocytic and bactericidal activities, but almost no chemotactic activity. Infection and fever in these patients seems to result from an inability to release and mobilise otherwise functionally normal neutrophils in the presence of bacterial stimuli. The precise receptor defect in these ” lazy leucocytes ” remains to be defined.