We have developed quantitative immunoassays for the intact, trimeric amino-terminal propeptide of human type I procollagen (PINP) and its Col1 domain. Intact PINP was isolated from the pleural fluids of cancer patients by a combination of ion-exchange, gel-filtration, and reversed-phase chromatographies. The amino-terminal Col1 domain of PINP was isolated after bacterial collagenase treatment of the heat-denatured trimeric propeptide. For the intact PINP assay we used a polyclonal antibody with only 1.2% cross-reaction with the monomeric Col1 domain. In human serum, this assay detects only one peak of PINP antigenicity that has the size of known intact PINP. Under similar conditions, an assay for the Coll domain of PINP recognized two circulating antigens. The biological relevance was further verified in wound fluid. Interassay and intraassay CVs were 3.1-9.3% for values within the reference intervals (mean +/- 2SD) for intact PINP in serum, which were 19-84 microg/L for women and 20-76 microg/L for men.