The solid-state structure of the semicarbazone derivative (3) of the aldehyde diacid (1), an acyclic diterpene isolated from Eremophila species, has been determined by a single-crystal room-temperature X-ray study. Crystals of (3) are triclinic, <P(1)over bar>, a 14.642(7), b 14.371(6), c 12.823(6) Angstrom, alpha 76.59(4), beta 66.09(4), gamma 72.97(4)degrees, Z = 4; R was 0.052 for 2265 independent 'observed' (I > 3 sigma(I)) diffractometer reflections.