The present thesis aimed to investigate the effects of psychological stress on the microbicidal potential of human macrophages in order to shed more light on the mechanisms that underlie stress-induced delays in the progress of wound healing. For this purpose, two studies were conducted. In a first study, we implemented an in vitro assay to assess the microbicidal potential of human macrophages. In a second study, we set out to examine the influence of an acute psychological stressor on the microbicidal potential of human macrophages within a wound paradigm. STUDY I Quantitative and qualitative changes in circulating leukocytes are known to be linked to psychological states. However, there is little information regarding comparable results with leukocytes in peripheral tissues, such as associations between the microbicidal potential of macrophages and psychological states. In this study, we implemented an inexpensive, simple-to-use and valid in vitro method for measuring the microbicidal potential of ex vivo isolated human monocyte-derived macrophages (HMDM). The method was implemented and validated using 21 healthy male subjects (M = 35.0 yrs; SEM = 2.32). The assay principle is based on the reduction of 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium (WST-1) by superoxide anions (O2-.), the first in a series of pathogen-killing reactive oxygen species produced by activated macrophages. First, freshly-isolated human monocytes were chemically stimulated to differentiate into macrophages. Subsequently, the HMDM were activated with phorbol 12-myristate 13-acetate to induce a microbicidal or O2- response. The WST-1 macrophage assay induced O2- responses by HMDM in all of the subjects. Furthermore, the WST-1 reduction scores correlated closely with results obtained by a reference method. The findings suggest that the in vitro method implemented investigates the microbicidal potential of ex vivo isolated HMDM in a simple, cost-efficient and val