At present, there is an increasing discussion regarding the change of the prostacyclin/thromboxane ratio as an aetiological factor of pregnancy-induced hypertension (PIH). By means of videophotometric capillaroscopy in the capillaries of the nailfold, it is possible to visualise the resulting changes in the microcirculation. This method employs a special illumination microscope (magnification of the optical system x 560). Red blood cell velocity is measured under test conditions and microcirculatorical reaction capacity on ischaemic stress. Studies were conducted on healthy non-pregnant women and on healthy pregnant women as well as on patients suffering from pregnancy-induced hypertension. A markedly reduced velocity of red blood cells in patients with pregnancy-induced hypertension was seen as a sign of vasoconstriction, namely, 0.53 mm/sec. versus 0.74 mm/sec. Furthermore, these patients have a higher reactivity to ischaemic stress, probably also as a result of the already existing vasoconstriction; however, the duration of the hyperaemic phases is reduced in pregnancy-induced hypertension. By this method, an insight can be gained into microcirculation in pregnancy and in pregnancy-induced hypertension. In addition, as preliminary studies have already shown, the influence exercised by different medications on microcirculation can be assessed.