An erythrocyte – like microorganism (ELM) was isolated in pure culture from 8 samples of blood taken from newborn umbilical cord, 50 samples of human blood for transfusion, and also in blood samples from 4 professors and 6 associate professors, who wanted to assure themselves in the discovery of new resident microbial flora, this time in human erythrocytes, about which there was no information in the medical literature. The size of ELM varied 1between 0.3 µm and 2.6 µm and because of this (with a size of 3.5 µm to 7.5 µm) 2 to 12 ELM cells could be seen (like in nest) in one erythrocyte after cultivation for 14 days at a temperature of 43°C in brain and heart liquid media. The electron microscope examination showed that ELM expulsed something like a cell nucleus being outside the human erythrocyte and it remained nucleus – free just like human red blood cells. This mimicry explained why ELM was able to multiply as a resident microbial flora in the human erythrocyte. ELM formed a unique red coating in the brain and heart media and very small grey colonies (which are almost invisible) on human blood agar after cultivation for 21 days at temperature 37°C, but not on sheep blood agar. Lysol as well as heat (70°C for 10 minutes) killed the ELM. The urease, lysine decarboxylase and catalase tests were positive. ELM produced acid from glucose and maltose, but not from sucrose and lactose. DNA could be demonstrated by the use of SDS polyacrilamide gel electrophoresis, but not by fluorescent stain because there was no nucleus in the ELM outside the erythrocytes. Sodium polyanetholsulphonate was bacteriostatic for ELM and due to this for the ELM isolation from blood the media should be prepared using sodium citrate.