A review of the available information on the toxicity and bioaccumulation of alkyphenols (AP) and their polyethoxylates (APE) and polyethoxycarboxylates (APEC) was conducted in support of their assessment as Priority Substances under the Canadian Environmental Protection Act. This included an examination of the acute and chronic toxicity of these compounds in a wide variety of aquatic organisms as well as an examination of their potential effects on endocrine function in fish and aquatic invertebrates. Although the data in the literature are scattered among many species, different test methods and chemicals, there is a consistent pattern in the toxicity. Nonylphenol (NP) and octylphenol (OP) are both acutely toxic to fish (17-3000 µg/L), invertebrates (20-3000 µg/L) and algae (27-2500 µg/L). In chronic toxicity tests no observable effect concentrations (NOEC) are as low as 6 mg/L in fish and 3.7 µg/L in invertebrates. There is an increase in the toxicity of both NPEs and OPEs with decreasing EO chain length. NPECs and OPECs are less toxic than corresponding APEs and have acute toxicities similar to APEs with 6-9 EO units. APs and APEs bind to the estrogen receptor resulting in the expression of several responses both in vitro and in vivo, including the induction of vitellogenin. The threshold for vitellogenin induction in fish is 10 µg/L for NP and 3 µg/L for OF. APEs also affect the growth of testes, alter normal steroid metabolism, disrupt smoltificaton and cause intersex (ova-testes) in fish. The available literature suggests that the ability of AP and APEs to bioaccumulate in aquatic biota in the environment is low to moderate, BCFs and BAFs in biota, including algae, plant, invertebrates and fish range from 0.9 to 3400. Although there are relatively few data available for OP or OPEs, their potential to bioaccumulate is expected to be similar to that of corresponding NP and NPEs.