Inter-alpha-trypsin inhibitor is composed of three distinct protein components. These protein components stem from independently encoded and proteolytically processed precursor proteins. Only the structure of the protein component responsible for the inhibitory activity has been established so far. We now present the complete amino acid sequence of the precursor of the second protein component derived from cloned cDNA. The precursor molecule includes both a signal peptide and a propeptide sequence and seems to be further processed prior to the assembly of the inter-alpha-trypsin inhibitor complex.