In the course of our investigation about ectromelia virus which began the year before last, we happen to percieve the appearance of intraplasmic inclusion bodies to a great extent in monocytes which were always recognizable in ascites by intraperitoneal inoculation of the virus emulsion. Thus, we were enable to investigate inclusion bodies in free single cells under supravital conditions entirely free from various artificial forces which had previous been used to gather cells in which were found inclusion bodies. So, we would like to report concerning inclusion bodies in monocytes in ascites which have been the special subject of our observation, as we have made use of such techniques as Giemsa's staining, and simple staining, dark field microscopy and ultra-violet photomicrography in supravital conditions. Quantitative and qualitative developement of inclusion bodies and cell reaction appear in the periphery zone of the cytoplasm having completely on reaction with centrosphere of monocytes, and increase their volume gradually. In supravital state the inclusion bodies stained positive with neutral red and fuchsin but negative with nilblue, brilliantcresylblue and bordeaux BX. Elementary bodies within the inclusion bodies having blue brilliant points were found in the supravital preparations by the dark ground microscope. It was possible to take ultraviolet photomicrographs of the infected monocytes in the supravital preparations. From data obtained by this method we observed the fine figures of elementary bodies in the ectromelia inclusion bodies corresponding to the blue points which had been found by the dark gorund microscope. Absorption of ultraviolet rays by inclusion bodies is much less than by the nucleis, and there is no difference between that of the inclusion bodies and that of the protoplasm. The results got from the ultraviolet microskopy coincide with the other results that the inclusion bodies give a negative Feulgen test in smear preparations.