111In-BLEDTA is a bleomycin-containing radiopharmaceutical that has proven useful as a tumor imaging agent. Whole blood distribution and pharmacokinetic parameters were studied in nine cancer patients, and the results compared with previously reported studies using 57Co-bleomycin. In eight patients studied by bolus intravenous injection, 111In-BLEDTA had a beta half-life (t1/2 beta) of 1.3 hours, a terminal-phase half-life (t1/2) of 11.7 hours, a volume of distribution (Vd gamma) of 57.5L/m2, a total body clearance rate (C1b) of 52.8 ml/min/m2, a renal clearance rate (C1r) of 23.3 ml/min/m2, and a 24-hour urinary excretion of 38.1% total administered dose. 111In-BLEDTA and 57Co-bleomycin have similar C1bs but differing Vds. Polymorphonuclear cell uptake of 111In-BLEDTA may explain its shorter t1/2 beta and t1/2, as well as its lower C1r and 24-hour urinary excretion. While the biologic characteristics of 111In-BLEDTA contribute to a greater background activity than is observed in scans with 57Co-bleomycin, its superior physical properties render it clinically more desirable as a tumor-imaging radiopharmaceutical.