Summary. Dimorphic yeast Trigonopsis variabilis is a uniquespecies that can form either an ellipsoidal or a triangular cell depending upon nutritional conditions. This fluorescence microscopic study was intended to correlate morphological changes of mitochondria in the triangular cells with the distribution of the cytoskeleton. In addition, unique features in the behavior of the cytoskeleton were also examined during triangular cell formation. In log-phase cells stained with 4',6-diamidino-2-phenylindole, mitochondrial nucleoids appeared as a string of beads throughout the vegetative growth. The profile of mitochondria stained by 3,3'-dihexyloxacarbocyanine iodide showed a network corresponding to the fluorescence images of mitochondrial nucleoids in both mother and daughter cells. Cellcycle-dependent fragmentation of mitochondria was not discerned. As the culture reached stationary phase, a network of mitochondria gradually changed to form unique rings that were located new the angles of triangular cells. When examined by immunofluorescence microscopy with anti-tubulin antibody, microtubules were found to be well developed along the sides of ceils in the cytoplasm of T. variabilis interphase cells. Although distributions of microtubules and mitochondria are different during cell cycle as a whole, cytoplasmic microtubules frequently extended along a part of the mitochondria in budded cells, suggesting correlation of microtubules and mitochondria. Rhodamine-phalloidin staining revealed both actin patches and cables. Actin cables elongated from mother cells into the buds and showed close proximity to mitochondria, although complete overlapping of both structures was rare. Moreover, actin patches localized on the mitochondrial network at a frequency of 65%. These results suggested that actin cables and patches, as well as microtubules, participated in the distribution of mitochondria. The localization of actin patches separated towards opposite ends at a bud tip when the bud grew to medium size. The unique localization of actin patches is responsible for bi-directional growth of the bud, forming triangular cells.