The MTZ (Molecule-Transform-Zap) notation (Leach et al., J. Chem. Inf. Comput. Sci. 1999, 39, 1161-1172), incorporating SMIRKS reactions and SMILES precursors, provides a flexible and powerful way of describing combinatorial libraries by the way they are made. However, it provides only an implicit representation of the product set, and enumeration and subsequent analysis of the individual products (e.g. using the enumerate program in contrib) can be slow. This talk will discuss how the reaction toolkit can be used to generate a Markush representation of a library, from which individual product SMILES, and other calculated properties (including fingerprints and Lipinksi properties) can be rapidly enumerated.