Phenolic compounds have been used because they are among the most toxic and ubiquitous environmental contaminants present in many industrial wastes. It is recognized that factors such as water hardness, pH, temperature, chemical formulation, species, age and/or stage of development of test organisms, to mention only a few, may critically affect the behavior of a chemical and thus effect the outcome of toxicity tests (Canton and Adema 1978; Berglind and Dave 1984; Persoone et al. 1989). Several studies dealing with the susceptibility of early life stages of invertebrates to pollutants have been reported in the literature (Middaugh and Dean 1977; Conklin and Rao 1978; Kaur and Dhawan 1993). An extensive literature review revealed information on the toxicity of different phenolic compounds to some species of fish and invertebrates. However, there is little information on acute toxicity of these compounds to different age classes of Artemia salina larvae. Artemia salina are of major importance in the aquaculture industry and they have been proposed as a uniform world-wide test system for toxicity of chemical substances (Vanhaeke et al. 1981) and for studies in developmental toxicology (Sleet and Brendel 1985). Previous investigations in this laboratory have shown that Artemia salina larvae exhibit increased sensitivity to certain chemicals in relation to aging. The present study was conducted to determine the acute toxicity of some phenolic compounds (pentachlorophenol (PCP), 2,6-dichloroindophenol (2,6-DCIP), 2,4-dinitrophenol (2,4-DNP), o-nitrophenol (o-NP), p-nitrophenol (p-NP), diamidophenol, diaminophenol and 2,6-dimenthylphenol (2,6-DMP) on Artemia salina 24-, 48- and 168- hr old to determine if changes in sensitivity occur during the first week after emergence.