Incubation of human mononuclear leukocytes (MNL) with human stroma-free hemolysate (SFH), purified adult hemoglobin Ao (HbAo), and oxidized HbAo (METHb) caused MNL to release compounds into the supernate that mediated neutrophil (polymorphonuclear leukocytes, PMN) chemotaxis and PMN adherence to human umbilical vein endothelial cells (HUVEC). Chemotaxis and PMN adherence to HUVEC were reduced significantly when supernates were preincubated with neutralizing antibodies to interleukin-8 (IL-8) and tumor necrosis factor alpha (TNF-alpha), respectively, suggesting that IL-8 and TNF-alpha played significant roles in mediating these activities. Greatest chemotactic activity was observed in supernates of MNL treated with HbAo; while greatest PMN/endothelial cell (EC) adherence activity was observed in supernates of MNL treated with METHb. Furthermore, PMN/EC adherence activity was a function of METHb content in each hemoglobin solution. PMN chemotaxis, PMN adherence to HUVEC, and cytokine release increased as a function of increasing incubation time. Chemotactic activity was detected in HbAo- treated and METHb-treated MNL supernates after incubation for 6 hours and was maximal by 10 hours. IL-8 was detected in both HbAo and METHb- MNL supernates by 4 hours. PMN/EC adherence activity was detected in HbAo-MNL supernates at 10 hours and in METHb-MNL supernates at 4 hours. TNF-alpha was detected in METHb and HbAo-MNL supernates at 4 and 12 hours, respectively. These results suggest that hemoglobin solutions stimulate MNL to release IL-8 and TNF-alpha in quantities sufficient to induce PMN chemotaxis and PMN adherence to HUVEC. This is a US government work. There are no restrictions on its use.