The haustorial fine structure of the bean rust fungus, Uromyces appendiculatus var. appendiculatus, was studied within the cells of its host, Phaseolus vulgaris. Results were obtained after high-pressure freezing and subsequent freeze-substitution or freeze-fracturing. Good preservation of leaf tissue after freeze-substitution needed cryoprotection with 8% methanol. For freeze-fracturing, no chemical treatment was applied. In addition to the organelles which are generally found in fungi after cryo-fixation, tubular-vesicular complexes were found in the cytoplasm. Both techniques revealed an extrahaustorial matrix of even width, surrounding the haustorial body. The extrahaustorial membrane was not undulated, and the side facing the plant cytoplasm was lined with a delicate fringe of well-stained material. The extrahaustorial membrane was nearly devoid of intramembrane particles. The host plasma membrane in infected tissue, especially the protoplasmic face, had fewer intramembrane particles than those in uninfected tissue. The haustorial plasma membrane contained many intramembrane particles.