ABSTRACT: The capping of lymphocytes from normal pregnant women is diminished. Decreased capping is observed for both anti-Ig and for Con A receptors. The altered capping response appears between the tenth and the twelfth week of pregnancy. The diminution in capping persists until about 2 weeks after delivery. The possible association between the decreased capping response and the altered immune responses known to occur during pregnancy is discussed. The factors underlying the altered capping response in pregnancy may be related to the factors responsible for the parallel phenomenon in pathological conditions.