- Being underweight is associated with a poorer outcome after haematopoietic stem cell transplantation (HSCT). We investigated whether nutritional status affects a patient's ability to mobilise stem cells. Weights, heights, peripheral blood CD34 counts and total collected stem cells were collected on 305 patients. Those patients who were underweight had a lower median peripheral blood CD34 count than those who were not underweight (36.0 vs. 53.0 × 10(6)/L (p = 0.0047)). However, the proportion of patients achieving a collection containing the minimum number of CD34 cells required to define a successful stem cell collection was similar in those who were underweight and those who were not. Therefore being underweight may reduce a patient's ability to mobilise peripheral blood stem cells and, if confirmed, improving nutritional status may reduce the number of patients who fail to mobilise.