Even small increases in the frequency of thrombotic disease in users of OCs have general health impact because of their widespread use, which is currently expanding to potential risk groups. The present investigations were launched to study the effects of OCs containing 20-40 micrograms of EE combined with the latest developed gonane progestogens on biochemical risk markers within metabolic systems involved in the development of arterial thrombotic disease. The studies included evaluation of carbohydrate and lipid metabolism as well as the haemostatic system and were performed in non-diabetic women and in women with IDDM, who are prone to the development of arterial thrombosis. In the evaluation of the carbohydrate metabolism in non-diabetic women, we found no effect on fasting glucose or insulin and no effect on the insulin response to oral glucose in women using monophasic OCs containing EE combined with DSG or GST. This contrasts the evaluation of triphasic OCs containing EE combined with GST or NGT, which increased fasting insulin and reduced insulin sensitivity without affecting the glucose-effectiveness or the beta-cell function. Impaired glucose tolerance developed in 10% of the women after 6 months. These finding suggest that OCs are able to induce a state of insulin resistance, which should be considered in the prescription for women with potential disturbed insulin sensitivity or reduced beta-cell secretory capacity e.g. women with ovarian hyperandrogenism, obesity, previous GDM or perimenopausal women. We found no change in glycaemic control in 22 women with well-regulated IDDM treated with a monophasic combination of EE and GST for one year and none of the women developed microalbuminuria during treatment. In the women with diabetes we observed an increase in fasting levels of triglycerides, a decrease in LDL-cholesterol, and unchanged concentrations of total cholesterol and HDL-cholesterol during treatment. In non-diabetic women treated with the same compound or an OC containing EE and DSG we found similar changes in triglycerides and total cholesterol, but increased levels of HDL-cholesterol and unchanged LDL-cholesterol concentrations. In the women with IDDM there was a negative correlation between daily insulin requirement and HDL-cholesterol before and during treatment, but no other statistically significant correlation between estimates of glycaemic control and lipids and lipoproteins were observed. In the non-diabetic women, changes in the haemostatic system included an increase in the procoagulant factors fibrinogen and Factor VIIc; the concentration of active t-PA increased, mainly because of decreased inhibition by PAI-1. The ratio between molecular markers of the activity of the coagulation system and the efficacy of fibrinolysis was unchanged. This was also found in the women with IDDM, who showed evidence of increased fibrin formation and an attenuated fibrinolytic response during treatment. The regulation of the t-PA/PAI system was studied in non-diabetic women in order to elucidate if the effects of OCs are caused by a direct effect on synthesis or clearance of these variables or if they are secondary to changed insulin sensitivity, as described in individuals with atherosclerosis. We found no indications that insulin resistance is involved in the regulation of t-PA and PAI-1 antigen levels, neither before nor during intake of OCs. We showed, however, that the decreased t-PA antigen concentration observed in OC users is caused by reduced synthesis outside the splanchnic circulation. The studies indicate that low-dose OCs containing newer gonane progestogens are able to induce insulin resistance and to impair glucose tolerance. Lipoproteins were not adversely influenced by the OCs neither in the diabetic nor the non-diabetic women; on the contrary, there was a tendency towards increased plasma levels of HDL-cholesterol and decreased LDL-cholesterol which are associated with a decreased risk of atherosclerosis. The changes observed within the haemostatic system were in accordance with a maintained balance between coagulation and fibrinolysis although the rate of fibrin formation may be increased in the women with IDDM. Irrespective of OC use, the interrelationships between metabolic systems in young non-diabetic women are different from those reported in individuals with atherosclerosis or insulin resistance. The effects of OCs on the t-PA/PAI system seem to be mediated by a direct effect on the vessel wall and not by changes in the hepatic clearance. The present findings were obtained in diabetic women without vascular complications, so the conclusion that women with IDDM can use OCs without metabolic alterations of known clinical significance is therefore restricted to those without evidence of diseased vessels. When evaluating the results obtained in the non-diabetic women, it should be remembered that women with recognised risk factors were excluded. The results may therefore be of limited value when evaluating the risk of arterial thrombosis in predisposed populations. In healthy individuals, the present integrated evaluation of biochemical markers does not indicate an increased risk of arterial thrombosis during use of low-dose OCs containing newer gonane progestogens; thus, the findings are in accordance with the recent epidemiological studies on these compounds. The application of relevant biochemical markers facilitate the understanding of the non-reproductive effects of sex steroids which have increasing importance because of their expanding use, not only as contraceptives, but also in the treatment of benign gynaecological disorders, as hormone replacement therapy and as prophylactic agents against specific degenerative conditions. Moreover, they may prove to be helpful in the future identification of women, who have increased susceptibility to the metabolic effects of sex steroids due to genetic predisposition.