A granulocytic Leukemic cell line, called L_(833), has been established through culturing in vitro frommouse bone marrow of transplantable granulocytic leukemia. More than 280 passages have been performedin 3 years. Cell growth has been rapid and stable. Incidence of tumour formation was 100% with variousroutes of inoculation. The nature of granulocytic leukemia was confirmed by examination of cytology,cytochemistry, pathology and ultrastructural changes. Analysis proved chromosomes to be hypodiploid with model number of 39, loss of chromosomes, andpresence of a marker. Besides the chromosomal change as mentioned above, both L_(883-A) and L_(833-B)derived from colonies formed from the L_(833) cells cultuerd in semi-solid agar medium, have their ownmarker. The cell line was sensitive to various types of antitumour agents in varying degrees. It was alsosensitive to ionizing radiation. D_0 values of L_(833) and L_(833-A) cells were 98.8 and 104.9 rad, respec-tively. The results were similar to that of L_(8 Cell growth has been rapid and stable. Incidence of tumor formation was established in vitro 100% with variousroutes of inoculation. The nature of granulocytic leukemia was confirmed by examination of cytology, cytochemistry, pathology and ultrastructural changes. Analysis of chromosomes to be hypodiploid with model number of 39, loss of chromosomes, and presence of a marker. Both L_ (883-A) and L_ (833-B) derived from colonies formed from the L_ (833) cells cultuerd in semi-solid agar medium, have their own marker. The cell line was sensitive to various types It was alsosensitive to ionizing radiation. D_0 values ​​of L_ (833) and L_ (833-A) cells were 98.8 and 104.9 rad, respec- tively. The results were simil ar to that of L_ (8