The following study records ten years' experience in the control of Fascioloides magna infection in a fenced area grazed by an overdense red deer population together with free-ranging cattle. During the winter 1977/78 mortality due to a "fascioloidosis-malnutrition syndrome" reduced the deer stock almost by half. Control measures were aimed at combatting the fluke in the wild definitive host by the administration of medicated pellets. Four flukicides were used over the years: rafoxanide, diamphenetide, oxyclozanide and triclabendazole. Efforts were also made to control the number of deer and to improve their condition by artificial feeding during the winter months. Intervention on the habitat of the intermediate hosts of F. magna were purposely avoided. The efficacy of this programme was evaluated by both copromicroscopic examinations and fluke counts from the livers of the wild and domestic macromammals living in the study area. Some yield parameters of the deer population were also taken into account. Results demonstrate that F. magna infection, though a hazard for cattle productivity, remained a deer problem when pharmacological prophylaxis was regularly applied.