Guayule (Parthenium argentatum Gray) is an interesting alternative and renewable source of rubber/latex which has been used in the past. Guayule rubber and latex products are not available in the market largely because the raw material cost is higher than the current sources produced in South-East Asia and other tropical countries (Hevea brasiliensis). Guayule contains many other compounds whose joint exploitation could make guayule cultivation profitable, especially in semi-desert areas where cultivation of other crops is difficult or impossible. Guayulins A–D, sesquiterpene esters, appear to have some commercial promise. Despite being accumulated in relatively high concentrations (its majority representative, guayulin A, can account for up to 13.7% of the resin content of this plant, which itself ranges from 6%–12%), guayulins have received little direct attention from scientists. This review presents the current knowledge about the activity of these compounds and, based on known activities of similar compounds from other species, potential uses as fungicides, miticides and insecticides are suggested.