The bioalteration produced by the action of different organisms on the materials used in the construction of monumental buildings is an important cause of their alteration process. This paper presents a biological, microbiological, and biochemical study of the stone alteration in the Cathedral of Seville. A first approach to the description of the organisms that colonize the stones by identification (plants, lichens), isolation and account in pure culture (algae, fungi), or identification by their metabolism products (sulfur and nitrogen cycle bacteria) has been made. Furthermore, analyses have been made to determine the biomaterial on the stone surface (BOD₅). See also <i>AATA</i><b> 26-380, 26-1130, 26-1154</b>, and<b> 26-1225</b> for related articles on the Cathedral of Seville. -- AATA