In this study we used Daphnia magna as an index organism for ecotoxicological studies. In order to determine the filtration and ingestion rates in Daphnia magna, we used algea Chlorella volgaris (10 mg/1). Prior to the tests, the acute toxicity of the herbicides Machete and Saturn and the pesticides Diazinon and Malathion, in order to calculate their EC50, were determined. The concentrations which caused the same mortality rate in 24 hours as the EC50 concentrations of these chemical did, were 18.49 mg/1 for Machete, 4.46mg/1 for Saturn, 0.31 gr/1 for Diazinon and 1.5 grit for Malathion. In order to study the toxic effect of Machete, Saturn, Diazinon and Malathion on the filtration and ingestion rates, Daphnia magna was exposed to Ec50, 3/4 Ec50 ,1/2 Ec50 and 1/4 Ec50 concentrations. The rates were reduced after the organism had been exposed to these toxic chemicals for 5 hours. The effective concentrations at which feeding rate were reduced by 50%, compared to the controls, were for herbicides activity and pesticides action. These values in regard to filtration and ingestion rates were 2.8 and 3.3 mg/1 for Machete, 1.45 and 1.6 mg/1 for Saturn, 0.16 and 0.075 mg/1 for Diazinon and 0.6 and 0.7 mg/1 for Malathion respectively.