Early changes in coagulation were found in patients following a paracetamol overdose. Low levels of clotting factors II, V and VII were present within 24 hours of the overdose. As the levels of factor II correlated with plasma fibrinogen values at this time, it is possible that they were consumed in the process of intravascular coagulation, although this was not supported by the presence of raised titres of fibrin degradation products. The prothrombin time ratio was greater than 2-2 within 30 hours of ingestion of the overdose in all patients who eventually died, whereas it was less than this in those developing only moderate liver damage. The administration of fresh frozen plasma to patients did appear to reduce the maximum abnormality of the prothrombin time ratio, which was significantly less three days after the overdose in the group receiving fresh frozen plasma. However, the coagulation disturbance was of short duration, and the prothrombin time ratio had also returned to normal within one week of the overdose in the control patients, and the administration of fresh frozen plasma did not appear to reduce the morbidity or mortality in the treated patients.