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Factor IX activity (IX:C) and antigen (IX:Ag) as well as factor VII, prothrombin time, Normotest and Thrombotest were determined in 37 haemophiüacs B from 26 kindreds, in 30 carriers of haemophilia B and in 40 healthy subjects. In 15 obligatory carriers from 9 kindreds, in which haemophiliacs did not exhibit IX:Ag in excess of IX:C, IX:C was parallel with IX:Ag, but in 4 from 4 kindreds, in which haemophiliacs exhibit excess of IX:Ag, there was a discrepancy between IX:C and IX:Ag. Among the obligatory carriers 6 from 3 kindreds, in which haemophiliacs did not have IX:Ag in excess of IX:C, showed that the anomaly M is not a sign of genetic variability of haemophilia B.

Antithrombin III (At-III) activity and protein, heparin cofactor activity, anti-factor Xa activity were determined in 200 healthy adults, evenly distributed within age and sex groups, in 60 patients with cerebral thrombosis and in 20 oral contraceptive users. There was a positive correlation between At-III protein and its activities in normal subjects and in patients with cerebral thrombosis, The mean At-III protein and heparin cofactor activity values decreased with age in men and in women of fertile age. The mean values of At-III protein and its activities did not show any variation in the patients with cerebral thrombosis when compared with the normals. In oral contraceptive users a positive correlation was also found between At-III protein and its activities, antifactor Xa activity excepted. The mean antifactor Xa activity value in these women decreased during treatment, whereas the other At-III activities and At-III protein were unchanged.