Although it is known that the advised or lower than advised doses of eco-friendly pesticides cause a genotoxic effect on non targeted higher cells as well as on targeted organisms, their very low or ultra low doses, however, have not been tested with an efficient method. The single cell gel electrophoresis (SCGE) or comet assay was used to detect the DNA damages on higher cells in vitro exposed to insecticides such as dimethoate (100-, 50-, 10 mu g ml(-1)), methyl parathion (90-, 45-, 5 mu g ml(-1)) alphacypermethrin (25-, 15-, 5 mu g ml(-1)) and dichlorvos (100-, 50-, 10 mu g ml(-1)) in which the concentration of each insecticide was designated as "very low volume" (vlv), "very very low volume" (vvlv) and "ultra low volume" (ulv) doses, respectively. The induction of DNA damage was evident on human peripheral lymphocytes (PBL) after 1 h treatment in vitro with the above insecticides. The results showed that the "vlv" and "vvlv" doses of methyl parathion (LD50=3 mu g ml(-1)), alphacypermethrin (LD50=57 mu g ml(-1)) and dichlorvos (LD50=50 mu g ml(-1)) caused significantly higher DNA damages in treated groups than those of their controls; on the other hand, dimethoate (LD50=387 mu g ml(-1)) caused a significant damage in blood cells only in "vlv" dose. DNA damage was not detected in "ulv" doses of all insecticides. It is probable that the "vlv" or "vvlv" doses of highly toxic chemicals expressing DNA damages on blood cells might be related with their very low LD50 values, which may play an important role on the impact of environmental pollution and human health even with their very low doses. It would be also beneficial to determine the genotoxic effect of "ulv" doses of all insecticides along with the non-harmful doses of dimethoate with extended incubation period if time has potential to create extensive DNA damages.