On the basis of a patient with fulminant meningococcaemia and severe disseminated intravascular coagulation (DIC) syndrome, the diagnostic potential of a clot impedance test - Sonoclot coagulation analysis - was used to evaluate plasma exchange. A 17-yr-old girl was treated for a fulminant infection with Neisseria meningitidis in our intensive care unit. She developed severe DIC. Whereas platelet administration caused immediate arterial oxygen desaturation necessitating ventilatory support, plasma exchange improved pulmonary and mental function. Three separate exchanges all improved haemostasis. Sonoclot analysis was used together with routine coagulation analyses to evaluate this DIC treatment. Sonoclot signs, such as lack of the shoulder and peak, prolonged shoulder-peak interval and peak time predicted clinical bleeding manifestations (haematuria, haemoptysis, epistaxis) and were improved by platelet transfusion and plasma exchange. Plasma exchange was successful even at a very low platelet count of < 23 x 10(9).L-1. Sonoclot coagulation analyses were normalised several days before routine coagulation analyses. The Sonoclot gave additional information to routine coagulation studies, correctly indicated insufficient haemostasis and predicted a positive outcome. Also, plasma exchanges and platelet transfusions could be controlled in the management of DIC.