The purpose of the present work was to analyze the presence of lysosomes in the syncytiotrophoblast of seven cultured and uncultured normal human placentas at term. An ultrastructural and ultracytochemical study for acid phosphatase was made by means of two techniques that employ different substrates, as well as morphometric studies. Two of the placentas were maintained "in vitro" for 48 h previous to their analysis. Scarce lysosomal dense bodies were located in the supranuclear region in relation to endocytotic vacuoles, specially in thinned off areas of the syncytiotrophoblast. The lysosomal population represented a 2.8% to 4.0% of the syncytial area. According to these results, it is suggested that human term placental lysosomes would participate in materno--fetal exchange.