About 30 years ago, Crosby wrote a commentary entitled “How Many ‘Polys’ are Enough?”, in response to an article on chronic idiopathic neutropenia by Kyle and Linman a few months earlier. 1, 2 Crosby described sharply contrasting events in two patients with no circulating neutrophils—one patient did well despite severe neutropenia, whereas the other had raging infections. His commentary emphasised that the risk and outcome of bacterial infections depend on an individual’s ability to respond to infection by delivering neutrophils to tissues, rather than the actual number of neutrophils in the peripheral blood.“Look for pus”, was his advice. Stain a sample of opportunistic body secretions and look for neutrophils. If they are missing, the patient is truly neutropenic and susceptible to infections. Despite Crosby’s wise advice, the problem of understanding neutropenia on a clinical, physiological, or molecular basis persists. Recently, HR Koene and colleagues reported a new method for assessment of susceptibility to infection in patients with chronic