Objective:To investigate the growth of H37Ra in the spleen and lung of mice.Methods:C57BL/6 mice were subcutaneously immunized with H37Ra and BCG respectively. At various intervals （15 days

30 days

60 days） after immunization

the spleen and lung of mice were isolated

dissociated and suitable dilutions of the homogenates were plated on Lowenstein-Jensen medium.The numbers of CFU were counted 18 days after incubation.Results:H37Ra (mean Log

10

CFU) locating in the spleen were 1.95

1.57 and 2.54;those growing in the lung were 1.37

1.08 and 0.94.The number of BCG locating in the spleen were 1.72

1.39 and 1.06;those growing in the lung were 1.16

0.96 and 0.50.At fifteenth and thirtieth days after immunization

the number of H37Ra and BCG locating in the spleen or lung did not show any significant difference （P

>

0.05）.But at sixtieth day after immunization

the number of H37Ra growing in the spleen or lung was significantly larger than those of BCG（P

<

0.05）.The number of H37Ra or BCG locating in the spleen were significantly larger than those growing in the lung（P

<

0.05）.Conclusion:H37Ra can exist at least for two months in the spleen and lung of C57BL/6 mice.