Safety of administration of a vindesine (VDS)-anti-CEA conjugate and its ability to localise after radiolabelling were investigated in patients with advanced metastatic carcinoma (4 colorectal and 4 ovarian). For imaging, patients received between 230 and 520 micrograms of 131I labelled antibody. In 5, localisation of conjugate was demonstrated, in another it was equivocal and in 2 patients, undetectable. For assessment of safety each patient also received a single dose of conjugate increasing from 1.2 to 42 mg antibody linked to 24 to 1800 micrograms VDS. The in vitro activity of the anti-CEA antibody and its ability to localise in vivo were preserved after conjugation. There was no obvious toxicity or hypersensitivity attributable to either the radiolocalisation or escalated doses of conjugate in any of the patients. The feasibility of the preparation and administration to patients of a vindesine-antibody conjugate has been demonstrated.