Marine unicellular algae, Skeletonema costatum, Thalassiosira pseudonana, and Chlorella sp., were exposed to the industrial brominated compounds, tetrabromobisphenol A (TBBP), decabromobiphenyloxide (DBBO), hexabromocyclododecane (HBCD), pentabromomethylbenzene (PBMB), pentabromoethylbenzene (PBEB), and the herbicide, bromoxynil (BROM), in six algal growth media. Saturation concentrations of DBBO (1 mg/1), PBMB (1 mg/1), and PBEB (0.5 mg/1) reduced growth by less than 50%. EC50s of the other compounds varied with growth medium, with high EC50/low EC50 ratios between 1.3 and 9.9. Lowest EC50s, 9.3 to 12.0 pi g/1, were obtained with S. costatum and HBCD. It is concluded that responses to toxicants in different media are the results of interactions between algae, growth medium, toxicant, and solvent carrier.