The impact of triazophos, bensulfuron-methyl, chlobenthiazone on soil biochemical characteristics in a paddy soil under controlled moisture (flooded soil) and temperature (25 degrees C) condition was studied. The electron transport system (ETS)/dehydrogenase activity displayed a negative correlation with triazophos, bensulfuron-methyl, chlobenthiazone concentrations, and the activity decreased as the concentration of the pesticides increased. The higher doses, 5 and 10 field rates, of triazophos, bensulfuron-methyl, chlobenthiazone significantly inhibited ETS activity, while lower rates failed to produce any significant reducing effect against the control. The relative toxicity of triazophos, bensulfuron-methyl, chlobenthiazone in decreasing the ETS activity was in the order: triazophos > chlobenthiazone > bensulfuron-methyl, irrespective of the rates of application. Triazophos, bensulfuron-methyl, chlobenthiazone caused an improvement in the soil phenol content and it increased with increasing concentration of triazophos, bensulfuron-methyl, chlobenthiazone. Triazophos, bensulfuron-methyl, chlobenthiazone incorporation did not produce any significant change in soil protein content. The response of biomass phospholipid content was nearly similar to ETS activity. The phospholipid content was decreased with the addition of triazophos, bensulfuron-methyl, chlobenthiazone in the order of triazophos > chlobenthiazone > bensulfuron-methyl; and the toxicity of applied amount was in the order: 10 FR (field rate) > 5 FR > 1.0 FR > 0.5 FR > control.