This paper reports the acute toxicity of three biocides used in the disinfection of cooling towers, tetrakis(hydroxymethyl) phosphonium chloride (THPC), trichloroisocyanuric acid (TCIC), and sodium bromide (NaBr), on Artemia larvae, their effect on the phototactic response of this organism, and the potential of bioaccumulation in this species. The 24-h median lethal concentration (LC50) values for these biocides with respect to 24-, 48-, and 72-h-old Artemia, determined by static bioassays, showed the following rank order of toxicity: THPC < TCIC < NaBr. An age-dependent increase in sensitivity was seen for each compound. All three biocides reduced the phototactic response of 24-h-old Artemia larvae in 24-h static bioassays; the median inhibitory concentration ratios obtained were 30 to 40 times lower than their respective 24-h LC50 values. The results suggest that phototaxis bioassays could provide the speed and simplicity required for screening many potential pollutants for harmful effects. The bioconcentration factors obtained for Artemia larvae exposed to 10% LC50 for 168 h in renewal assays were 93.75, 1.67, and 0.23 for THPC, TCIC, and NaBr, respectively. This shows these biocides pose no bioaccumulation risk in this organism, although the value of 93.75 obtained for THPC is close to the threshold above which such a risk is considered to exist.