The response of a few members of freshwater micrometazoans to DDT have been ascertained by conducting laboratory and field bioassay experiments. The organisms tested in laboratory bioassays, have been found to respond at low concentrations with LC50 ranging between 10 and 49 ppb.Cyclops sp. andAsplanchna brightwelli respond to higher concentrations of DDT with LC50 as high as 515 ppb and 2218 ppb respectively LC50 for the larvae ofCulex fatigans has been found to be 180 ppb. In the field test of 70 ppb of DDT was applied and repeated after 23 days. The response of organisms is similar in both the treatments. The population ofC. cornuta andM. brachiata reappeared after 22 days of the treatment whereas,D. excisum andN. kamakhiae failed to reappear. Analysis of the bottom soil of the treated tank revealed the presence of DDD, DDE and DDT. Some secondary effects of the DDT treatment have also been observed and discussed.