['Interstitial pneumonia (IP) associated with CTDs often progresses despite conventional immunosuppressive treatment. We investigated the efficacy of human urinary trypsin (UT) inhibitor (ulinastatin) on refractory IP.', 'Five patients with IP received UT inhibitor (3 x 10(5) U) infusion into the internal jugular vein, three times in a single day. The response to this therapy was assessed clinically and by chest CT, PaO(2) and serum KL-6. The kinetics of UT inhibitor was determined in arterial blood. We measured serum levels of monocyte chemotactic protein-1 and TGF-beta1, which are thought to be involved in the pathogenesis of IP.', 'Serum concentrations of UT inhibitor increased immediately to >150 U/ml after infusion of 3 x 10(5) U of UT inhibitor. The treatment resulted in clinical and radiological improvements in four patients, and allowed reduction of oxygen therapy following improvement of hypoxaemia within 1 month. UT inhibitor decreased serum levels of KL-6 in all patients and had no adverse effects. MCP-1 and TGF-beta1 concentrations were higher in the patients than in normal subjects, and infusion of 3 x 10(5) U of UT reduced the concentrations within 3 h of infusion.'] Does bolus infusion of human urinary trypsin inhibitor improve intractable interstitial pneumonia in patients with connective tissue diseases?