Volatile oils of Citrus sinensis, Ageratum conyzoides, Cymbopogon citratus, Callistemon rigidus and Ocimum gratissimum were tested as repellents against blackfly, Simulium damnosum s.l., the vector of human onchocerciaisis. Topical applications of 10 and 20% v/v concentrations of the oils with liquid paraffin as the carrier, were made on the forearms and legs of four volunteers, with ordinary paraffin oil used as the control. At 10% v/v concentration the protection time was between 30min and 1h with the Citrus, Ageratum, Cymbopogon and Callistemon oils. At 20% Citrus, Ageratum and Cymbopogon oils repelled the blackflies for up to 2h while Callistemon and Ocimum oils were effective for 3h. Application of these volatile oils, especially at the peak biting periods, would serve to reduce human–vector contact and thereby limit disease transmission.