Calcium signaling via calmodulin and calcineurin is critical for the regulation of stress responses in fungi. The functions of calmodulin and calcineurin are largely conserved among pathogenic fungi and model fungi, however, the mechanisms of action have diverged. Saccharomyces cerevisiae is an excellent model for understanding the framework of calcium-mediated signal transduction pathways, and considerable progress has been made in understanding the details of how Ca2+-calmodulin and calcineurin control adaptation to environmental stress. Studies using the divergent human pathogenic fungi Candida albicans and Cryptococcus neoformans reveal that calcineurin is critical for virulence, yet it acts via distinct mechanisms in each fungus. These differences in function may reflect the requirements of each pathogen to survive inside the host, and illustrate that studies must be conducted in each organism in order to elucidate the details of the molecular mechanisms of calmodulin and calcineurin-mediated signaling pathways. (C) 2003 Elsevier Inc. All rights reserved.