A study on chromosome of leucocytes in blood cultures derived from 6 normal Korean was performed . Exact chromosome counts were carried out on 205 cells in male, 211 in female , of which 86.05% revealed a chormosome mordal number of 46. On the basis of relative chromosome lengths and position of centromeres, the Karyotype that the human chromosomes were classified into 7 groups with 22 airs of autosome and one pair of sex chromosome was determined accoridng to the method of denver report. The chromosome number on metaphase was observed in short term cultures of leucocytes from the peripheral blood of 2 patients with chronic granulocytic leukemia and 1 patient with acute granulocitic leukemia . and the chromosome morpholoogy was also investigated in one acute leukemic patient. In all leukemic cases the leucocytes showed the constant value of 46 in the stem -line of chormosome number. But the frequency of cells with 46 chromosomes appeared in the 3 cases was 67.30% in average with a slightly higher range in hypo-andhyper-diploid chromosome numbers than in normal human, The idiogram analysis did not show any abnormality of chromosome in acute leukemic cells.