The clearances of 125I-labeled alpha 1-proteinase inhibitor-trypsin, antithrombin III-thrombin and alpha 2-macroglobulin-methylamine (CH3NH2) were compared in our previously described mouse model. alpha 1-Proteinase inhibitor-trypsin cleared with a t 1/2 of 20 min, antithrombin III-thrombin of 7 min and 125I-labeled alpha 2-macroglobulin-methylamine of 2 min. Competition studies were performed to determine whether one or several pathways clear these three ligands. The clearance of 125I-labeled alpha 1-proteinase inhibitor-trypsin and 125I-labeled antithrombin III-thrombin was blocked by large molar excesses of either ligand, but not by alpha 2-macroglobulin-methylamine. The clearance of 125I-labeled alpha 2-macroglobulin-methylamine can be blocked by a large molar excesses of unlabeled alpha 2-macroglobulin-methylamine but not by alpha 1-proteinase inhibitor-trypsin. These studies demonstrate that the clearance of alpha 1-proteinase inhibitor-trypsin complexes is independent of alpha 2-macroglobulin-methylamine and utilizes the same pathway which is involved in the clearance of antithrombin III-thrombin complexes.