Warts, hypogammaglobulinaemia, infections, myelokathexis (WHIM) syndrome is an inherited immune disorder associated with CXCR4 gene mutations. Recent studies suggested that impaired receptor downregulation and enhanced chemotactic responsiveness to stromal-derived factor-1 (SDF-1), the sole cognate ligand for CXCR4, may account for the characteristic features of WHIM patients. This study evaluated whether the interaction of SDF-1 with CXCR4 could block constitutive apoptosis of peripheral blood neutrophils from congenital neutropenia patients and controls. SDF-1 was found to be a potent anti-apoptotic factor for WHIM neutrophils harbouring a truncating CXCR4 mutation, but not for neutrophils from control individuals, thus supporting the notion that such mutations may confer enhanced functional responses.