Serum concentrations of soluble ICAM-1 (sICAM-1) were studied in patients with acute myeloid leukemia (AML) after conventional dose consolidation chemotherapy and in AML and in breast cancer patients following high dose chemotherapy with autologous haematopoietic stem cell transplantation. Investigations were carried out at 3 phases following treatment; during the chemotherapy induced neutropenic phase (neutrophil counts <0.5x109/l); during early recovery (neutrophil counts 0.5x109/l-1.0x109/l); and at recovery from neutropenia (neutrophil count 1.0x109/l-2.5x109/l). Results showed a significant elevation of serum levels of sICAM-1, above normal, in both groups of patients during the neutropenic phase. A further increase of sICAM-1 was found in conventional dose consolidation chemotherapy treated AML patients during the post-neutropenia recovery phases. By contrast, patients who were treated with high dose chemotherapy plus autologous haematopoietic stem cell transplantation showed a normalisation of sICAM-1 concentration during the post-neutropenic recovery phases. These findings suggest that recovery of neutrophil function do not coincide with recovery of neutrophil count following intensive chemotherapy while rapid recovery of neutrophil function occurred among patients who received autologous haematopoietic stem cell support.