Comparative toxicity of several pesticides, lindane, endosulfan, pentachlorophenol (PCP), 3,4‐dichloroaniline (DCA) and copper sulphate has been tested to determine their lethality in two species of freshwater invertebrates,Daphnia magnaandBrachionus calyciflorus. D. magnawas more sensitive thanB. calyciflorusto all the toxicants tested except to copper sulphate. DCA was the most toxic compound toD. magnaand was followed in order of decreasing toxicity by copper sulphate, PCP, endosulfan and lindane. Copper sulphate was the most toxic chemical tested to the rotiferB. calyciflorusand was followed by PCP, endosulfan, lindane and DCA. The 24 hr LC50 values (mg/L) forD. magnaandB. calyciflorus,respectively, were: lindane, 1.64 and 22.5; endosulfan, 0.62 and 5.15; DCA, 0.20 and 61.5; PCP, 0.39 and 2.16; copper sulphate, 0.38 and 0.076.