The analysis of known drugs (Comprehensive Medicinal Chemistry database (2008 version): http://www.mdl.com/products/knowledge/medicinal_chem/index.jsp ) and natural products (Koch et al., Proc Natl Acad Sci USA 102:17272-17277, 2008) has led to the identification of privileged saturated and aromatic heterocyclic ring pairs that we have termed as "BioCores." This article explains how the BioCores can be used for the design of novel lead-like scaffolds.