The plasma fibrinogen concentration of 47 healthy individuals was measured in order to determine the reference range for our laboratory, which was calculated to be 1.75-3.31 g/l. The plasma fibrinogen concentration of 44 hospital patients was also measured for comparison. These patients were selected because they were free from bleeding tendency and liver disease. The distribution of their fibrinogen levels was Gaussian, but more wide-based than the distribution of our normal controls. The mean fibrinogen value of the patient group was 3.60 g/l, significantly higher than that of the healthy group, which was 2.53 g/l. The reasons why the fibrinogen distribution graph of patients assumed such a pattern and the role of fibrinogen in health and disease are discussed.