Chitin synthase genes of Tuber magnatum were sought in order to investigate the molecular bases of its growth. Primers designed from highly conserved Chs domains were used to identify a chs gene portion. A genomic library was used to obtain the full gene sequence (TMchs4) with an open reading frame which encodes a predicted protein of 1230 amino acids. The sequence is similar (62%) to the class IV chitin synthase from Neurospora crassa. The putative protein shows hydrophobicity pattern that suggests the presence of several intramembranous domains and other peculiar features common to the other chs of class IV. Northern experiments demonstrated that the gene is expressed in ascomata sampled at different maturation steps. These data suggest that ascomata growth requires new chitin deposition, which is based on a chs gene activation and not only on an enzymatic activity.