Green monkeys (Cercopithecus aethiops), experimentally infected with the causative agent of the Frankfurt-Marburg-Syndrome (FMS-virus), were killed after the appearance of disease symptoms, and. nephrectomized. Tissue cultures were set up from the trypsinized kidney tissue. Examination of live tissue culture under low magnification revealed no difference in rate of growth or appearance from the cultures of kidney cells from non-infected monkeys. Intracytoplasmic eosino-philic inclusion bodies could be found invariably in stained preparations of the cells of kidney tissue cultures deriving from infected monkeys, virus particles could be seen by electron microscopy, and viral antigen could be demonstrated in the cells with immunofluorescent antibody technique. That the tissue culture fluids contained infectious virus could be demonstrated by inoculating monkey kidney cell tissue cultures in stationary growth phase and observing the cyto-pathic effect.