In two open randomized studies carried out in female volunteers the effects of a new low dose oral contraceptive (O.C.) combination desogestrel + ethinylestradiol (150 micrograms/30 micrograms; Marvelon) on blood coagulation were compared with those of either the combination levonorgestrel + ethinylestradiol (150 micrograms/30 micrograms) or a triphasic preparation containing levonorgestrel + ethinylestradiol. A total of 78 women were involved in the studies which covered a period of 4 cycles; a pretreatment cycle followed by 3 treatment cycles, each consisting of 21 days of drug administration, followed by a 7-day tablet-free period. A blood sample was taken before treatment, after 2 weeks, 2 cycles and 3 cycles of treatment. The following parameters were measured: prothrombin; activated partial thromboplastin time; factors VII, VIII, X; fibrinogen; antithrombin III; euglobulin lysis time; platelet count and aggregation ratio; triglycerides and cholesterol and a glucose tolerance test was made. The effects of the different preparations on these parameters were compared statistically using either an analysis of covariance or the Wilcoxon test. No clinically significant differences were observed between the desogestrel containing preparation and the two other preparations. Any changes in treatment versus pretreatment values were slight and in agreement with the literature on other O.C.'s.