Chlamydospore formation of the fungal pathogen Candida albicans was found to depend on the Efg1 protein, which regulates the yeast-hyphal transition. Isogenic mutants lacking EFG1 or encoding T206A and T206E variants did not differentiate chlamydospores, while cek1, cph1, or tpk2 mutations had no effect. Furthermore, filamentation of efg1 cph1 double mutants in microaerophilic conditions suggests a novel Efg1p/Cph1p-independent filamentation pathway in C. albicans.