The essential oils extracted from Eucalyptus grandis, Eucalyptus camaldulensis, Eucalyptus tereticornis, and the hybrids E. grandisxE. camaldulensis, and E. grandisxE. tereticornis were analyzed by GC-MS, and evaluated for their fumigant and repellent effects on permethrin-resistant head lice. Fumigant activity of both hybrids was higher than that for pure species. E. grandisxE. tereticornis and E. grandisxE. camaldulensis showed KT50 values of 12.99 and 13.63min, respectively. E. grandis, E. camaldulensis, and E. tereticornis showed KT50 values of 25.57, 35.01, and 31.31, respectively. A simple regression analysis revealed a significant correlation between KT50 data and % of 1,8-cineole in these essential oils. Repellency varied from 47.80+/-16% to 80.69+/-6% for the five Eucalyptus essential oils tested. Interspecific hybridization improves the pediculicidal activity of Eucalyptus essential oils.