Alterations in immunological response before and after chemotherapy were investigated in hamsters infected with A. ceylanicum. Four reference anthelmintics mebendazole, albendazole, levamisole and pyrantel pamoate and one newly synthesized anthelmintic compound 81-470 were used. Drugs in curative doses were administered on day 30 post infection and the humoral response was assessed by counter immunoelectrophoresis and ELISA and cell mediated immunity by delayed type of hypersensitivity reaction. In infected untreated animals the precipitins appeared on day 30 and remained prominent till day 250 post infection. However with ELISA the antibodies could be demonstrated as early as day 3 post infection and peaked on day 40. Delayed type of hypersensitivity could not be demonstrated during the course of infection. All the drugs including Comp. 81-470 were effective in removing the parasites. Precipitin antibodies were only demonstrable till day 60 post treatment. ELISA depicted gradual depletion of antibody titre following treatment with mebendazole, albendazole and pyrantel pamoate. In levamisole treated hamsters the initial fall in serum antibody was restored by day 20 post treatment. With Compound 81-470, immediately after the treatment there was sharp rise in antibodies concentration followed by gradual fall and on day 60 post treatment the titre was still higher than the pretreated titre. Thus the study denotes that effective therapy will bring down immune responses of the host if the drug possess no immunopotentiating action. Therefore the immune parameters may be used as supportive indicator to successful therapy particularly in systemic parasites where parasitic forms are nondemonstrable in excreta or blood.