AbstractAn electron microscope study of experimental and environmental lead poisoning of leaf cells from the mossRhytidiadelphus squarrosus(Hedw.) Warnst. is described. Plants treated with lead acetate and lead chloride solutions, or collected from roadsides exposed to lead pollution from motor exhaust gases have been used. The results are compared with other studies of experimental lead poisoning in both plants and animals, with particular regard to uptake mechanisms and to lead accumulating at different sites in the cell. We have shown that lead may be bound within the cell wall, and that it may also enter the cytoplasm. Pinocytosis was observed in leaf cells from moss plants treated with lead salt solutions. Via pinocytotic vesicles within the cytoplasm the particles containing lead could then be discharged into the vacuole. In the leaf cells of mosses exposed to environmental pollution the protoplasmic lead was found to be bound within the nucleus, and was easily identified as electron-dense, nuclear inclusions.