Table I.

Prevalence of factor V Leiden carriers in the considered cohorts of subjects

Group	Subjects	Normal		Heterozygous		Homozygous
		N.	%	N.	%	N.	%
A	229	129	56.3	88	38.9	11	4.8
B	234	175	79.8	55	23.5	4	1.7
C	231	201	87.1	29	12.6	1	0.4
D	240	214	89.2	25	10.4	1	0.4

Group A: 229 subjects studied after a venous thrombosis

Group B: 234 blood relatives of the patients enrolled in group A

Group C: 231 women before prescription of oral contraception

Group D: 240 repeat male blood donors