Ectodesmata were visualized in outer epidermal cell walls of Nicotiana tabacum (L.) var. T.I. 787 by means of a silver nitrate stain and electron microscopy. After inoculation of potato virus X (PVX), neither whole virus nor viral RNA could be observed in ectodesmata by means of direct observations in the electron microscope. Fully assembled virus particles were seen attached to, but not penetrating, the cuticle of inoculated tobacco leaves.