We investigated the inhibition of granulocyte phagocytosis by 8-MOP and monochromatic or polychromatic UV light. After application of 8-MOP and UV there was an additional inactivation compared with UV alone, as expected from studies on other cell species. This additional inhibition of phagocytosis was found to be increasing with 8-MOP level. The action spectra of granulocyte inactivation by 8-MOP and UV involves the investigated UVB range (until 300 nm). A marked inactivation of granulocytes was seen after erythemogenic fluences only. Therefore we assume that inactivation of granulocytes by direct UV action does not play an essential role in UV therapy in vivo.