[Dimorphic fungi: biochemical approach to their dimorphism].

Dimorphism in pathogenic fungi is reviewed. The phenomenon is divided into four interwoven events: (a) perception of external stimuli by cellular sensors; (b) translation into a biochemical message; (c) alteration of the genomic expression, and (d) structural reorganization towards the morphological change. Experimental evidence is provided. Finally, the possibility that fungal dimorphism may have arisen multiple times throughout evolution, is discussed.