One of the main purposes in current computational lexicography is to determine methods to allow the acquisition of lexical knowledge. One of the facilities of the Acquilex Lexical Knowledge Base is the possibility of defining lexical rules. These rules are used for generating new lexical entries from the existing ones, capturing linguistic generalizations which will be reflected in the new entries. The main goal of this paper is the treatment of Spanish verbal subcategorization alternances (diatheses) by means of lexical rules. Different subcategorization schemes can be generated from the most basic (or general) verbal entry by applying lexical rules which show the diverse morphological, syntactic or semantic changes produced.