Juniperus communis leaf oil, J. chinensis wood oil, and Cupressus funebris wood oil (Cupressaceae) from China were analyzed by gas chromatography and gas chromatography-mass spectrometry. We identified 104 compounds, representing 66.895.5% of the oils. The major components were: a-pinene (27.0%), a-terpinene (14.0%), and linalool (10.9%) for J. communis; cuparene (11.3%) and d-cadinene (7.8%) for J. chinensis; and a-cedrene (16.9%), cedrol (7.6%), and beta-cedrene (5.7%) for C. funebris. The essential oils of C. funebris, J. chinensis, and J. communis were evaluated for repellency against adult yellow fever mosquitoes, Aedes aegypti (L.), host-seeking nymphs of the lone star tick, Amblyomma americanum (L.), and the blacklegged tick, Ixodes scapularis Say, and for toxicity against Ae. aegypti larvae and adults, all in laboratory bioassays. All the oils were repellent to both species of ticks. The EC95 values of C. funebris, J. communis, and J. chinensis against A. americanum were 0.426, 0.508, and 0.917 mg oil/cm2 filter paper, respectively, compared to 0.683 mg deet/cm2 filter paper. All I. scapularis nymphs were repelled by 0.103 mg oil/cm2 filter paper of C. funebris oil. At 4 h after application, 0.827 mg oil/cm2 filter paper, C. funebris and J. chinensis oils repelled =80% of A. americanum nymphs. The oils of C. funebris and J. chinensis did not prevent female Ae. aegypti from biting at the highest dosage tested (1.500 mg/cm2). However, the oil of J. communis had a Minimum Effective Dosage (estimate of ED99) for repellency of 0.029 +/- 0.018 mg/cm2; this oil was nearly as potent as deet. The oil of J. chinensis showed a mild ability to kill Ae. aegypti larvae, at 80 and 100% at 125 and 250 ppm, respectively.