Geraniol is a bioactive component found in Palmarosa essential oil which has previously demonstrated good repellence to cattle ticks, mosquitoes and sand flies. The toxicity of geraniol to Dermanyssus gallinae, the most economically deleterious ectoparasite of laying hens in Europe, was studied in vitro in the laboratory. Exposure of D. gallinae to 0.5, 1 and 2% concentrations of geraniol (equating approximately to 0.02, 0.04 and 0.07 mg/cm2 geraniol, respectively) over a period of 24 hours resulted in 100% mortality of D. gallinae at all doses used.