A study involving the obstetric clinic population of 3 major teaching hospitals of Karachi has been conducted to define changes in leucocyte and platelet counts as pregnancy progresses. 573 "normal" pregnant women--183 in the first trimester, 195 in the second trimester and 194 in the third trimester were included in this analysis. We have found leucocytosis to be a feature of normal pregnancy; the change is subsequent to a progressive increase in granulocytes. Platelet counts were found to decrease slightly as pregnancy progresses.