The aim of this work is to study bio-distribution and tumor absorption of anti breast cancer monoclonal antibody 6C6 and its chimeric antibody 6C6-CHI. The modified Schwartz method was employed to label 6C6 and 6C6CHI with 99Tcm. The labeled antibody was injected to mouse via tail vein and the blood clearance and whole body clearance were observed. Nude mice bearing breast cancer MCF7 cells were injected with 99Tcm-Iabeled antibodiy and the bio-distribution was studied and imaged with γ-ray camera. The yield of the two labeled antibodies was more than 90% and their immunoactivities were more than 80%. The whole body eliminated half-time of 99Tcm-6C6 was 4.1h

and the half-times in blood were rα=0.55h and rβ=12.42h respectively. The whole body half-time of 99Tcm-6C6CHI was 4.28h and the half-times in blood were Tα=0.98h and Tβ=12.42h respectively. The bio-distribution of nude mice bearing breast cancer MCF7 cells was as follows: the ID%/g of tumor and blood was （7.42±0.85） and （5.67±1.44） respectively at 23h after injection of 99Tcm-6C6. The T/NT （tumor to non tumor） ratios were all more than 1.0 except kidney and the ID%/g of tumor and blood was （4.23?.64） and （6.97?.23） respectively at 23h after injection of 99Tcm-6C6CHI. The T/NT （tumor to non tumor） ratios were all more than 1.0 except blood and kidney. The y imaging results showed that the tumor was imaged clearly at 24h after injection of radiolabled antibodies and the other organs did not concentrate the antibodies except kidney. Anti-breast cancer monoclonal antibody 6C6 can be well located in tumor. Although ID%/g of tumor of the chimeric antibody 6C6CHI was slightly lower than that of 6C6 antibody

and ID%/g of blood was higher than that of 6C6

the tumor imaging of 6C6-CHI was also clear.