In vivo imaging system (IVIS) is a new and rapidly expanding technology, which has a wide range of applications in life science such as cell tracing. By counting the number of photons emitted from a specimen, IVIS can quantify biological events such as tumor growth. We used B16F10-luc-G5 tumor cells and 20 Babl/C mice injected subcutaneously with B16F10-luc-G5 tumor cells (1x10(6) in 100 mu L) to develop a method to quantitatively analyze cells traced by IVIS in vitro and in vivo, respectively. The results showed a strong correlation between the number of tumor cells and the intensity of bioluminescence signal (R (2)=0.99) under different exposure conditions in in vitro assay. The results derived from the in vivo experiments showed that tumor luminescence was observed in all mice by IVIS at all days, and there was significant difference (P < 0.01) between every two days from day 3 to day 14. Moreover, tumor dynamic morphology could be monitored by IVIS when it was invisible. There was a strong correlation between tumor volume and bioluminescence signal (R (2)=0.97) by IVIS. In summary, we demonstrated a way to accurately carry out the quantitative analysis of cells using IVIS both in vitro and in vivo. The data indicate that IVIS can be used as an effective and quantitative method for cell tracing both in vitro and in vivo.