It is possible that the phenotypic analysis of depleted lymphocyte subtypes at day 1 may improve the sensitivity of the day 1 model: in a recently reported study, patients with both day 1 CD4+ and CD56+ lymphopenia were found to be at high risk for FN in a series of 226 patients (Blay et al, 2001). The gene discussed is CD4; the disease is lymphopenia.