Methods and reagents for improved treatment and diagnostic imaging, particularly of cancer. The methods and reagents utilize specific targeting of treatment and imaging ligands to the targeted tumor, or specific organ or tissue, in association with extracorporeal affinity adsorption of the targeting ligand. The targeted species include antibodies as well as other peptides with specific affinity to the targeted tumor organ or tissue. Included are hybrid targeting molecules, such as hybrid F(ab').sub.2, with one binding site specific for the target and the other binding site specific for the targeted treatment or visualization ligand. The affinity adsorption devices may include adsorbents specific to one or more of the components of the targeting molecule-targeted ligand moiety. The methods provide for improved treatment, particularly in cancer and HIV, by increasing the concentration in the tumor and decreasing the concentration in the rest of the body, thus reducing its toxicity and enabling the use of high doses of drugs and other treatment agents. Improved visualization of cancer is provided by increased concentration of visualization ligand in the cancer and reduced concentration in the blood and normal tissues.