Here, we describe two cases of severe pyogenic infection in healthy donors diagnosed immediately following stem cell mobilisation with G-CSF. In the first donor a painful perianal abscess and in the second one an apical abscess required surgical incision. The reported serious adverse events in the literature are reviewed and the potential pathophysiological role of G-CSF or GM-CSF in augmenting inflammatory processes is discussed. In the light of a rapidly increasing number of related and unrelated peripheral blood stem cell donations the need for more comprehensive donor work-up and follow-up for peripheral blood stem cell donors has to be considered. Bone Marrow Transplantation (2000) 26, 811-813.