We previously studied fibrinolysis and fibrinogenolysis by analyzing fragments of fibrin/fibrinogen degradation products (FDP) employing sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting. In this report, we characterized the fragments of FDP in three patients with increased serum FDP, that were caused by various diseases. In the patient suffering from tuberculous constrictive pericarditis (case 1), the most part of the FDP fragments were DD and D. In the patient suffering from infection in addition to liver cirrhosis (case 2), the most part of the FDP fragments were high molecular weight (HMW) and D. In case 1 and 2, serum FDP levels were increased in parallel with the elevations of CRP levels. Although DD and HMW fragments were remarkably increased in case 1 and 2 with our immunoblotting analysis, DD levels assayed with LPIA system were much lower than FDP levels. The reason this discrepancy was explained by the observation that affinities of the monoclonal antibody used in LPIA system with DD and HMW fragment were markedly lower than that to DD-E fragment. In the patient suffering from deep vein thrombosis probably caused by steroid therapy of nephrotic syndrome (case 3), the most part of detected FDP fragments were DD and HMW in the period when APTT was shorter than normal, whereas D was mainly observed in the period when APTT was normal. In case 3, FDP and DD levels were increased in parallel with the shortening of APTT. In these non-DIC patients, increased serum FDP levels were induced by the presence of ascites and/or pleural effusion plus infection.(ABSTRACT TRUNCATED AT 250 WORDS)