The effect of kerosene and BP 1002 upon the naupliar and adult stages of Balanus amphitrite amphitrite and Balanus variegatus variegatus has been studied. The percentage non-motility and actual mortality of the naupliar larvae and the adults of both species has been generally shown to be a function of the dosage and treatment time of these two hydrocarbons. Both barnacles (nauplii and adults) have a similar susceptibility to the hydrocarbons tested, the nauplii being killed at lower concentrations than the adults. Cirral activity of the adults was significantly reduced when the barnacles were treated with 10 and 100 ppm BP 1002. Preliminary experiments have also been performed to compare the toxicity of BP 1002 and kerosene with that of 'Bukomkleen' and 'Chemkleen'. It was found that BP 1002 was the most toxic to these barnacles with a lower and similar toxicity found for Chemkleen and Bukomkleen. The toxicity of kerosene is comparatively low. Copyright © 1977 Published by Elsevier Ltd.