The etiological factors leading to pregnancy induced hypertension are still obscure, but it has been understood that vasoconstriction due to increased vascular reactivity to pressor agents might be involved in the pathogenesis of preeclampsia. However, the circulating levels of pressor or fluid-retaining agents related to the renin-angiotensin system, aldosterone, deoxycorticosterone or antidiuretic hormone have been reported to be normal or even reduced in pregnancy induced hypertension. Recently links have been established between prolactin and pregnancy induced hypertension by several investigators. Stumpe et al suggested that prolactin might be implicated in some hypertensive states, possibly by altered central dopamine control. On the other hand, Horrobin et al stated that prolactin can influence the vascular response to pressor agents and a reduced prolactin response might be the cause of increased sensitivity to the pressor agents observed in preeclampsia. Along these lines, there are several reports concerning the plasma concentration of prolactin in preeclamptic patients. However, consistent changes in the plasma prolactin levels have not been observed to make any positive statements regarding the role of prolactin in the pathogenesis of pregnancy induced hypertension. In view of the several reports documenting that prolactin may modulate vascular reactivity to pressor agents, this study was undertaken to compare prolactin concentrations in the plasma of normal and preeclamptic pregnancies and to ascertain the possible role of prolactin in the pathogenesis of pregnancy induced hypertension. A total of 40 cases with preeclampsia and as controls, 40 normotensive healthy women between 38 and 42 weeks gestation were involved. Statistically both groups were comparable in respect to the patients` age, parity and duration of pregnancy. Plasma prolactin was assayed by a double antibody radioimmunoassay. The plasma prolactin level in controls was 223±15ng/ml in average and 54 to 427ng/ml in range, and that in preeclampsia mean plasma prolactin value seemed to be slightly higher than that in controls but there was no significant difference between two groups(g>0.05). Mean plasma prolactin level of 285±35ng/ml in severe preeclampsia were somewhat higher than that of 235±27ng/ml in mild preeclampsia, but no significant difference could be observed between mild and severe preeclampsia (p>0.05). These results suggest that other factors rather than prolactin may participate in increasing the vascular reactivity to pressor agents in pregnancy induced hypertension.