Two laminin-derived peptides containing either YIGSR or IKVAV (single amino acid code) sequences were radiolabeled with 99mTc and their biological distribution evaluated in rodents. Both 99mTc-peptides cleared rapidly from the circulation though the kidney, and to a lesser extent, through the liver. 99mTc-YIGSR peptide did not accumulate in any organ examined in normal, tumored, and emphysemic mice. The 99mTc-IKVAV peptide localized within 10 min to the lung of normal animals, resulting in lung-to-blood ratios of approximately 23:1. The 99mTc-IKVAV peptide localized to lung after submicron filtration and after intraperitoneal injection, suggesting that particulates do not major role in localization. Pre-incubation of 99mTc-IKVAV peptide in whole blood decreased lung localization, suggesting that margination of radiolabeled cells does not play a major role in the lung localization. When 99mTc-IKVAV was injected into mice with tumored lungs (melanoma), the lung uptake was markedly increased (up to 20% injected dose higher than control lungs) at all time points examined (10, 30, and 120 min). When 99mTc-IKVAV was injected into mice with genetic emphysema, the lung uptake was markedly decreased at all time points. The localization of the 99mTc-IKVAV-containing peptide to the lung is consistent with a receptor-based mechanism.