Objective     To explore the fluorescent distribution

and the relation between fluorescent intensity and time after injecting rear-thigh muscles with DiI.      Methods     Sixty-five new born mice were equally and randomly divided into 13 groups. Fluorescent distribution and intensity were investigated at 2

4

6

8

12

24 h

and 2

4

7

14

28 d and 2

3 months after injecting the left posterior limb rear thigh muscles with 1.5 μl  4 mg/ml DiI for one mouse.      Results     The labeling neurons were scattered from L

2

level to S

2

level and associated dorsal root ganglion （DRG）

but the most were located at L

4

to L

6

section. The faint red fluorescenc

e neurons were observed at dorsal root ganglion and cornu anterius medullae spinalis 6 h post-injection. The labeling neurons increased up to the 4th day. The fluorescent intensity enhanced gradually from 6 h to 24 h

then kept the intensity for 3 months.      Conclusion     It is a quick

precise

persistent method to trance and label the dorsal root ganglions sensory neuron and spinal motoneuron by injecting rear-thigh muscles with DiI

and the rate of labeling neurons can be improved by prolonging the tracing time properly. It is also provide basic data for clinical or experimental neuron label and location.