Efficacy of doramectin administered via oral and parenteral routes against experimentally induced and natural infections of the copepod parasite Lernaea cyprinacea in carps was studied. Administration of doramectin incorporated in feed at 1mg/kg b.wt. of fish for 10 days effectively controlled experimentally induced Lernaea infection in Labeo fimbriatus fingerlings within an average of 19 days of post-treatment as compared to the normal course of 41 days. Similarly, doramectin given through feed at 1mg/kgb.wt. of fish for 10 days was equally effective in controlling natural infection of this parasite in the underyearlings of Catla catla and L. fimbriatus. Intramuscular administration of doramectin at 200microg/kgb.wt. of fish effectively removed adult Lernaea infection in L. fimbriatus as early as 18 days of treatment as compared to the time period of 43 days taken by the untreated fish to get rid of the infection. Single intramuscular administration of the drug was more effective against the parasite than its administration in multiple divided doses. In all cases, doramectin did not cause any noticeable adverse reactions or toxicity to the fish host. In view of the handling associated stress and other operational difficulties involved, a single intramuscular administration of the drug at 200microg/kgb.wt. is suggested for treatment of heavily infected adults and brood stock of carps. Doramectin incorporated in feed at 1mg/kgb.wt. of fish is best suited for treatment of Lernaea infection in young fish including fingerlings. However, detailed studies on the toxicity and pharmacokinetics of doramectin upon its administration to aquatic organisms and the environmental impact of its usage are required to be undertaken before finally recommending the safe use of this drug for control of parasitic infections of aquatic organisms.