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The present study was undertaken to evaluate the median lethal concentration (LC50), morphological deformities and changes in behavioural responses caused by commercial formulations of malathion on Duttaphrynus melanostictus tadpoles. The LC50 value was found to be 7.5 mg/l and ability of malathion to cause morphological anomalies and changes in behavioural responses in tadpoles were studied at sublethal concentrations of 0.5 mg/l (1/15th), 0.75 mg/l (1/10th) and 1.5 mg/l (1/5th) for a duration of 5 days. The morphological defects and changes in behavioural responses like notochord curvature and loss of fright response respectively were witnessed as an important conduct; in addition, other symptoms under both the parameters were known to be time (i.e. developmental stage) and concentration dependent thereby acknowledging the direct cause of damage due to malathion. Thus, based on the present study, care must be taken when this chemical is in use at agricultural sites especially nearby aquatic ecosystems.