The repellency of the essential oil of the previously reported anti-tick pasture shrub Gynandropsis gynandra and identi®ed constituents of the oil were evaluated against the livestock tick, Rhipicephalus appendiculatus. In a tick-climbing repellency bioassay, the oil of G. gynandra exhibited a repellency eect which at the highest treatment levels was higher than that of the commercial arthropod repellent N,N-diethyltoluamide. Twenty eight compounds were identi®ed in the G. gynandra oil by GC, GC-MS and coinjection with authentic samples. Carvacrol was found to occur in largest quantity (29.2%), followed by transphytol (24.0%), linalool (13.3%), trans-2-methylcyclopentanol (7.2%) and b-caryophyllene (4.4%). m-Cymene, nonanal, 1-aterpineol, b-cyclocitral, nerol, trans-geraniol, carvacrol, b-ionone, trans-geranylacetone, and nerolidol were the most repellent components against R. appendiculatus. Methyl isothiocyanate which occurred in the G. gynandra oil at a relative percentage of 2.1 and which was not tested in the bioassay due to its toxicity may also contribute signi®cantly to the repellency of the oil. The repellency of the oil of G. gynandra supported earlier ®ndings by other workers that G. gynandra repelled R. appendiculatus ticks.