Encoded combinatorial organic synthesis has recently emerged as a powerful tool for the discovery of biologically active compounds from complex chemical libraries. This report describes a new encoding methodology that uses chemically robust secondary amines as tags. These amines are incorporated into an N-[(dialkylcarbamoyl)methyl]glycine-coding oligomer through simple chemistry that is compatible with a wide range of polymer-supported transformations useful in combinatorial synthesis. In the decoding process acidic hydrolysis of the tagging polymer regenerates the secondary amines, which after dansylation are resolved and detected at sub-picomole levels by reversed-phase HPLC. The versatility of this strategy is demonstrated here by encoded syntheses of members of several representative heterocyclic compound classes, including beta-lactams, 4-thiazolidinones, and pyrrolidines.