A substance eremolactone (C20H26O2) from Eremophila freelingii, obtained via prolonged steam-distillation of leaves, is identified as a diterpene of a new biogenetic type. Evidence regarding parts of its structure is provided through spectral examinations (ultraviolet, infrared, proton magnetic resonance) and chemical reactions (alkaline hydrolysis, hydrogenation, oxidation, ozonolysis, etc.). Based on the evidence, biogenetic hypotheses, and Bredt's rule, formula (XI) is suggested as the best working hypothesis for eremolactone. Due to lack of material and Dr. P. R. Jeffries' work on similar compounds from other Eremophila species (one identical to eremolactone in melting point, optical rotation, and infrared spectrum), further work in this field is discontinued.