Monensin, an exocytosis perturber, was assayed on the dimorphic fungus Candida albicans in order to study its effects on wall synthesis and morphogenesis. In the presence of the drug, both germ-tube formation and hyphal elongation were markedly inhibited according to the dose and exposure time. The effect was accompanied by morphogenetic malformations which could be detected under UV light and by transmission electron microscopy. Enormous wall and septa thickenings revealed by cytochemical tests indicated an abnormal deposition of chitin. Since chitin synthase is inserted in the plasma membrane in a latent state and its activation depends on regulatory factors reaching the cell periphery through an orderly exocytosis, it is assumed that monensin affects the vesicular traffic leading to a prevalence of activators over inhibitors of the enzyme.