Proline is an amino acid that possesses a pyrrolidine moiety, and relatively few alkaloids are known or considered to be derived directly from proline, with these alkaloids possessing either a pyrrolidine or a pyrrole moiety in their structures. A number of alkaloids that appear to be derived from proline (e.g., chlorophyll, heme, kainic acid, nicotine) are actually derived through other biosynthetic pathways. In this chapter, prodigiosin (from the cultured broth of Serratia marcescens), stachydrine (from Fabaceae plants), and pyrrole-2-carboxylic acid (from the culture broth of Streptomyces sp. No. 82–85) are described. Labeled proline is established to be incorporated into prodigiosin and stachydrine, and pyrrole-2-carboxylic acid may be derived from proline although there is no direct evidence.