The occurrence and fate of additives in the aquatic environment is an emerging issue in environmental chemistry. This paper describes the ecotoxicological effects of the commonly used additive butylated hydroxyanisole (BHA) using a test battery, comprising of several different organisms and in vitro test systems, representing a proportion of the different trophic levels. The most sensitive system to BHA was the inhibition of bioluminescence in Vibrio fischeri bacteria, which resulted in an acute low observed adverse effect concentration (LOAEC) of 0.28 microM. The next most sensitive system was the immobilization of the cladoceran Daphnia magna followed by: the inhibition of the growth of the unicellular alga Chlorella vulgaris; the endpoints evaluated in Vero (mammalian) cells (total protein content, LDH activity, neutral red uptake and MTT metabolization), mitotic index and root growth inhibition in the terrestrial plant Allium cepa, and finally, the endpoints used on the RTG-2 salmonid fish cell line (neutral red uptake, total protein content, MTS metabolization, lactate dehydrogenase leakage and activity, and glucose-6-phosphate dehydrogenase activity). Morphological alterations in RTG-2 cells were also assessed and these included loss of cells, induction of cellular pleomorphism, hydropic degeneration and induction of apoptosis at high concentrations. The results from this study also indicated that micronuclei were not induced in A.cepa exposed to BHA. The differences in sensitivity for the diverse systems that were used (EC50 ranged from 1.2 to >500 microM) suggest the importance for a test battery approach in the evaluation of the ecological consequences of chemicals. According to the results, the levels of BHA reported in industrial wastewater would elicit adverse effects in the environment. This, coupled with its potential to bioaccumulate, makes BHA a pollutant of concern not only for acute exposures, but also for the long-term.