The uptake of peroxidase by cultured human trophoblast-cells was monitored ultrastructurally. There was no apparent effect on the distribution of peroxidase caused by treatment at 4 °C, with KCN or with IgG. Pinocytic channels penetrate deep into the perinuclear cytoplasm and may act to allow pinocytosis to occur within layers of microfilaments which might otherwise prevent pinosome access to the majority of the synthetic organelles.