Objectival. To prepare a radioimmunoguided surgery （RIGS） system including radio-nuclides hand- held gamma detecting probe （GDP） with signal processing control unit

specific monoclonal antibody （MAb）

technique of labeling as well as detection of ovarian carcinoma in nude mice bearing human ovari-an carcinoma. Metals. MAb COCl83B

2

produced in our laboratory was used to prepare the F （ah’）

2

fragment by ficin digestion.

99m

Tc labeling of COC183 B

2

-F（ab’）

2

and normal mice IgG were prepared according to im- proved pretining method. GDP and control unit were made by Chinese Atomic Energy Research Institute. Different groups of nude mice bearing human ovarian carcinoma with ascites were administered with differ- ent dosages of

99m

To COCl83 B

2

-F（ab’）

2

and their tissues measured by GDP in vivo and compared with gamma well counts after dissection in vitro. Results.

99m

Tc labeled COCl83B

2

-F（ab’）

2

yielded a labeling rate of over 90%

and a good immunoac- tivity. The detections of carcinoma tissue by GDP showed a T/NT ratio of 2: 1 as positive for cancer. The smallest carcinoma detected was 0. 2cm × 0.1 cm and the nearest distance between carcinoma and normal tissue was 0. 2cm. Conclusions. The above studies proved that ficin can be used to digest MAbs with high yields and good immunoactivity of F（ab’）

2

. Our RIGS system with

99m

To labeled COC183 B

2

-F（ab’）

2

and GDP can hope-fully be used clinically for ovarian carcinoma detection.