To compare the immune response in normal and pathological pregnancy, some functions of phagocytic cells were studied in 8 women with pre-eclampsia and 7 healthy women matched for age and parity. Free oxygen radical activity determined by chemiluminescence (CL) of polymorphonuclear leukocytes (PMN) and monocytes (MN) during phagocytosis of preopsonized zymosan, and cell migration measured by tube migration of PMN were studied together during and after pregnancy. CL of MN decreased or remained unchanged during normal pregnancy, but a marked increase was observed in pre-eclampsia. CL of PMN increased, too, in the pre-eclamptic patients, but the difference was not significant. Tube migration was enhanced during pregnancy compared with baseline values, but the values were significantly lower in the pre-eclamptic group. Immuno-globulins (Ig G, Ig M and Ig A) were studied in both groups. A decline in Ig G level from baseline to the 3rd trimester was observed in patients. The complement fractions C3 and C4 were not altered during pregnancy in any group. The study indicates a difference in behavior of phagocytic cells in normal vs. pre-eclamptic pregnancy.