Observations on the ultrastructure and function of the so-called "microfold" or "membraneous" cells (M cells) by means of peroxidase as a tracer.

79 NMRI mice and Wistar rats were used for ultrastructural investigations of the sequential uptake of horseradish peroxidase (HRP) by M cells. In addition the ultrastructure of the so-called tuft-cells was reported.