[en] Differences of pharmacokinetics and tumor imaging ability between intact monoclonal antibody A7 (A7 MoAb) and F(ab)₂ fragments were studied in human colon cancer (LS-174T)-bearing nude mice. The authors examined the yield and the immunoreactivity of F(ab)₂ fragments after treatment with ficin as a function of time. The yield of F(ab)₂ fragments reached about 50% after ficin treatment for 8 h, and the F(ab)₂ retained about 80% of the immunoreactivity of the corresponding MoAb. Longer digestion with ficin produced smaller fragments (less than 92 kDa) with a lower yield and most of the immunoreactivity was lost. In pharmacokinetics studies, the F(ab')₂ was preferentially taken up by the tumor, cleared more rapidly from the blood circulation and seemed to have less non-specific tissue binding than intact A7 MoAb. The tumor image obtained at an early time using ¹³¹I-F(ab')₂ was much superior in quality to that with intact ¹³¹I-A7 MoAb. The use of F(ab')₂ fragments may be effective for tumor diagnosis and therapy. (author)