Fungal chitin synthases are classified into seven classes. Recent advances in genome sequence analyses have revealed that there are more than seven chitin synthase-encoding genes in the genome of filamentous ascomycete fungi. To clarify the functional differences among these genes in the morphogenesis and hyphal tip growth, we have cloned six chitin synthase-encoding genes from Aspergillus nidulans and analyzed their functions. The results obtained suggest that chitin synthases are structurally and functionally divergent and play crucial roles in the growth and morphogenesis of A. nidulans.