The paper deals with the toxicity of a surfactant-based oil dispersant to the ATPase activities of two naupliar stages of Artemia (instar I & II). Both instars were exposed to sub-lethal and lethal concentrations derived from acute toxicity data. The chosen concentrations were near to LOECs and NOECs. An eightfold difference indicated between the instars was instar-exposure time dependent. The most prominent effects were the inhibition and the stimulation of Na+/K+-ATPase and Mg2+-ATPase activities, respectively. The cause of these effects was related to the dispersant components, the surfactants. The pattern stimulation/inhibition of Mg2+-ATPase and Na+/K+-ATPase activities could be used to indicate toxic stress by surfactant-based oil dispersants since previous studies with other contaminants have shown different ATPase activity patterns.