Administration of high-dose cytotoxic therapy with autologous bone marrow transplantation (BMT) results in prolonged cytopenia and significant morbidity and mortality. Several groups have reported that the administration of recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) to patients with delayed haematological recovery following autologous BMT may accelerate neutrophil recovery and decrease mortality. We have determined the prevalence and natural history of delayed neutrophil recovery following BEAM chemotherapy and autologous BMT for malignant lymphoma in 261 patients treated at a single institution without the use of haemopoietic growth factors. Forty of 261 (15%) patients took > 28 days to reach an absolute neutrophil count (ANC) > 0.5 x 10(9)/L; 29 of these 40 (73%) with delayed engraftment reached an ANC > 0.5 x 10(9)/L by day +42. Five patients with delayed engraftment died before day +100, two of progressive lymphoma, one from unirradiated blood product-related GVHD and two of interstitial pneumonitis (IP). The patients with IP had negative culture and bronchoscopic examinations and onset of assisted ventilation was day +15 and +18, respectively. These results show a high rate of relatively rapid spontaneous recovery in individuals with delayed neutrophil recovery after BEAM plus autologous BMT with a low incidence of death from infection.