An examination of the biokinetics and biodistribution of i.p. administered 131I- or 111In-labelled 791T/36 antibody (1 mg) has been carried out in five patients with stage III/IV ovarian cancer. Blood kinetics and urinary excretion of the radiolabels were assayed. Scintigraphy was performed immediately following administration and before and after peritoneal lavage at 48 h. Blood levels of both preparations rose over the first 20-40 h reaching 8-14% of the administered dose in the circulation and then declined (T1/2 of 40 h). Circulating radiolabel was still attached partially to antibody as shown by precipitation with anti-mouse IgG antiserum. The rapid appearance of radiolabel in the bloodstream meant that any tumour localization could be from circulating antibody rather than local infiltration. Interpretation of the images was difficult and the distribution of the tracer was different from that previously observed using i.v. administration of antibody. In some cases the images were confusing and the uptake of activity did not fit in with the clinical knowledge of the disease or the findings from laparoscopy. Tumour specimens resected at 4-5 days showed up to 0.02% of the dose g-1.