Robenidene has appreciable anticoccidial activity against Eimeria brunetti and E. tenella in chickens. In the case of E. tenella under continuous drug medication, this activity has been shown to be primarily coccidiostatic at the stage of the almost mature first generation schizont. The stage at which the drug acts was predicted from the mortality pattern in experiments involving restricted administration of drug and confirmed by histological examination of caeca from treated birds and by observation of parasites in tissue culture.