A quantitative, light microscopic morphometric model for uptake of particulates by Peyer's patch M cells was developed. Rabbit intestinal loops containing Peyer's patches were inoculated with fluorescent, non-degradable polystyrene microparticles (600-750 nm), and their localization in Peyer's patches was traced after varying time periods. The particles were localized sequentially at the FAE cell surface, spanning the entire width of FAE cells, and within the subepithelial dome as a function of time. The particles were associated with 5D9+ or 1D9+ M cells, but were not taken up or transported by villus epithelia. The kinetics suggested a synchronous wave of uptake and transepithelial transport. Quantitative analysis revealed a considerably greater uptake efficiency of polystyrene microspheres in comparison to other biological particles.