The bioactivity of 14 essential oils from five plants has been studied using the brine shrimp lethality test and the Aedes aegypti larvicidal assay. All essential oils screened had LC50 values smaller than 200 mug/ml, showing significant lethality against brine shrimp. In addition, nine of the 14 essential oils tested showed toxicity against the fourth-instar A. aegypti larvae in 24 h (LC50 < 100 mug/ml). Of these, the leaf and bark essential oils of Cryptomeria japonica demonstrated high larvicidal activity, the most active being the leaf essential oil of C japonica, with a LC50 = 37.6 mug/ml (LC90 = 71.9 mug/ml), followed by the bark essential oil of C japonica also showing high activity against A. aegypti larvae, with a LC50 = 48.1 mug/ml (LC90 = 130.3 mug/ml). The results obtained from this study suggest that the leaf and bark essential oils of C japonica are promising as larvicides against A. aegypti larvae and could be useful in the search for new natural larvicidal compounds.. (C) 2003 Elsevier Science Ltd. All rights reserved.