Guayule is a woody desert shrub that produces natural rubber, cis-1,4-polyisoprene, by biosynthesis. It is currently cultivated in the southwestern United States as a source of latex and rubber for commerical development. Guayule latex is similar to Havea latex in polymer molecular weight and microstructure, and in many colloidal properties. Important differences exist, however, in rubber extractable and insoluble components; most notably protein content.