To further understand human host defenses against Trichosporon beigelii, functional responses were investigated of polymorphonuclear leukocytes (PMNL) and elutriated human monocytes (EHM) to this opportunistic fungal pathogen. There was significantly less PMNL phagocytosis (P < .001) and killing (P < .001) of T. beigelii isolates than of Candida albicans. However, levels of superoxide anions generated by PMNL in response to T. beigelii and C. albicans were comparable. Pretreatment of PMNL with granulocyte colony-stimulating factor or interferon-gamma (IFN-gamma) did not significantly enhance fungicidal activity. Killing of T. beigelii by EHM also was significantly impaired compared with killing of C. albicans (P < .001). However, pretreatment of EHM with macrophage colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, or IFN-gamma all resulted in enhanced fungicidal activity. Thus, phagocytosis and killing of T. beigelii by PMNL and EHM are significantly less efficient than that of C. albicans. However, monocytes may be more important in the control of Trichosporon species than previously shown.