The effects of three common agrochemicals, lindane, methyl parathion and atrazine, on crustacean Daphnia magna, alga Selenastrum capricornutum and marine bacterium Vibrio fischeri were investigated in this study. Methyl parathion was the most toxic compound towards all three organisms, while lindane was more toxic to Daphnia magna and Vibrio fischeri than atrazine, and atrazine was more toxic to Selenastrum capricornutum than lindane. Among the three aquatic organisms, Selenastrum capricornutum was most sensitive in detecting lindane and atrazine toxicity, while Daphnia magna was most sensitive in detecting methyl parathion toxicity. The interactive effects of the pesticides were also investigated. The interactive effect between lindane and methyl parathion on survival of Daphnia magna was synergistic, while the ones between lindane and atrazine and between methyl parathion and atrazine were generally additive. The interactive effect of the three pesticides applied together on Daphnia magna was synergistic. The interactive effect of the three pesticides on the growth of Selenastrum capricornutum was antagonistic with few cases of addition, while the effect of all the three pairs of pesticides on algal growth was also antagonistic. The interactive effect of lindane and methyl parathion on Vibrio fischeri was additive.