The well-known coagulation inhibitors antithrombin and protein C, and the more recently described inhibitors, heparin cofactor II and extrinsic pathway inhibitor, were measured in plasma during a 7-day observation period, from patients with pneumonia (n = 13), and in stroke patients with infarction (n = 9) and haemorrhage (n = 9). In patients with pneumonia, elevated fibrinopeptide A levels and subnormal antithrombin and protein C levels suggested some degree of consumption of the inhibitors. Later, an increase was observed for all the inhibitors, but was most conspicuous for heparin cofactor II which reached high normal values. C-reactive protein, initially markedly elevated, decreased rapidly. This finding suggests that heparin cofactor II might act as a delayed acute phase reactant. In stroke patients only small, not statistically significant, changes occurred during the observation period, except for heparin cofactor II which increased in patients with haemorrhagic stroke.