Plasma fibrinogen and plasminogen levels were measured in 122 male and 56 female healthy adult subjects and in 64 men with ischaemic heart disease. Plasma fibrinogen levels were found to rise markedly and progressively with age in both male and female healthy subjects; plasminogen showed only a slight rise with age. No sex differences were found for either fibrinogen or plasminogen. The correlation between plasminogen and fibrinogen levels was low, reaching the 5% level of significance only in men. Patients with ischaemic heart disease were found to have significantly increased fibrinogen and plasminogen levels in the 31-45 years age group only.