Human lung cancer cells (ASTC-a-1) were infected with EGFP plasmid vectors, and incubated in RPMI 1640 culture medium supplemented with 15% FCS and 800 mg/L G418. Strong fluorescence of five cell clones were observed after several generations. The flow cytometry was used to determine the GFP expression stability, the results showed that there was significant difference between 2#(3#) and 4#(5#) (P＜0.01). The nude mouse, 6 weeks of age, was injected s.c. with a single dose of 3×10⁶ infected tumor cells. The GFP fluorescence was directly exited by 488 nm argon ion laser and recorded by digital camera with 530 nm long pass filter.