Wegener's granulomatosis (WG) is a systemic vasculitis which is diagnosed on clinicopathological findings. The diagnosis may be aided by the presence of anti-neutrophil cytoplasm antibodies (ANCA). In WG, ANCA are primarily directed to proteinase 3 (PR3), a serine protease of the azurophilic granules of the neutrophilic granulocyte. The main plasma inhibitor of PR3 is alpha 1-proteinase inhibitor (PI). To study if free PR3 or complexes between the enzyme and PI or PR3 and ANCA could be found in the plasma from patients with WG we have developed three ELISA systems for the detection of these complexes and free PR3. In all three assays monoclonal antibodies against PR3 were used as capture antibodies. After incubation with plasma, free PR3 was detected by affinity purified rabbit anti-PR3 followed by alkaline phosphatase-labelled swine anti-rabbit IgG. Serial dilutions of purified PR3 was used as standard. The detection limit was 3 ng/ml. PR3 complexed with PI was measured by rabbit anti-PI antibodies and alkaline phosphatase-labelled swine anti-rabbit IgG. Pre-formed in vitro complexes of PR3/PI in serial dilutions were used as standard. The detection limit of this assay was 1 ng/ml. PR3/IgG-ANCA complexes were detected by alkaline phosphatase labelled goat anti-human IgG. A positive plasma sample in serial dilutions was used as standard. Plasma samples from nine patients with WG, eight patients with fever of infectious origin without evidence of vasculitis and ten healthy donors were examined by these methods. Free PR3 could not be found in any of the plasma samples. PR3/PI complexes were detected in healthy donors at levels between 41-85 ng/ml. All WG patients, both active and inactive, had PR3/PI concentrations above this level, and so had all patients with fever. PR3/IgG-ANCA was found in three of the patients with WG, two being ANCA negative with inactive disease and one was ANCA positive with active disease. Thus, the developed methods can be useful for future studies of the clinical relevance of these complexes in patients with WG and possibly other vasculitides.